| Message ID | 20230118224505.1964941-8-david@fromorbit.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
| Series | xfs: per-ag centric allocation alogrithms | expand |
On Thu, 2023-01-19 at 09:44 +1100, Dave Chinner wrote: > From: Dave Chinner <dchinner@redhat.com> > > We need to be able to dynamically remove instantiated AGs from > memory safely, either for shrinking the filesystem or paging AG > state in and out of memory (e.g. supporting millions of AGs). This > means we need to be able to safely exclude operations from accessing > perags while dynamic removal is in progress. > > To do this, introduce the concept of active and passive references. > Active references are required for high level operations that make > use of an AG for a given operation (e.g. allocation) and pin the > perag in memory for the duration of the operation that is operating > on the perag (e.g. transaction scope). This means we can fail to get > an active reference to an AG, hence callers of the new active > reference API must be able to handle lookup failure gracefully. > > Passive references are used in low level code, where we might need > to access the perag structure for the purposes of completing high > level operations. For example, buffers need to use passive > references because: > - we need to be able to do metadata IO during operations like grow > and shrink transactions where high level active references to the > AG have already been blocked > - buffers need to pin the perag until they are reclaimed from > memory, something that high level code has no direct control over. > - unused cached buffers should not prevent a shrink from being > started. > > Hence we have active references that will form exclusion barriers > for operations to be performed on an AG, and passive references that > will prevent reclaim of the perag until all objects with passive > references have been reclaimed themselves. > > This patch introduce xfs_perag_grab()/xfs_perag_rele() as the API > for active AG reference functionality. We also need to convert the > for_each_perag*() iterators to use active references, which will > start the process of converting high level code over to using active > references. Conversion of non-iterator based code to active > references will be done in followup patches. > > Note that the implementation using reference counting is really just > a development vehicle for the API to ensure we don't have any leaks > in the callers. Once we need to remove perag structures from memory > dyanmically, we will need a much more robust per-ag state transition > mechanism for preventing new references from being taken while we > wait for existing references to drain before removal from memory can > occur.... > > Signed-off-by: Dave Chinner <dchinner@redhat.com> ok, I was able to follow it Reviewed-by: Allison Henderson <allison.henderson@oracle.com> > fs/xfs/libxfs/xfs_ag.c | 70 > +++++++++++++++++++++++++++++++++++++++ > fs/xfs/libxfs/xfs_ag.h | 31 ++++++++++++----- > fs/xfs/scrub/bmap.c | 2 +- > fs/xfs/scrub/fscounters.c | 4 +-- > fs/xfs/xfs_fsmap.c | 4 +-- > fs/xfs/xfs_icache.c | 2 +- > fs/xfs/xfs_iwalk.c | 6 ++-- > fs/xfs/xfs_reflink.c | 2 +- > fs/xfs/xfs_trace.h | 3 ++ > 9 files changed, 105 insertions(+), 19 deletions(-) > > diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c > index bb0c700afe3c..46e25c682bf4 100644 > --- a/fs/xfs/libxfs/xfs_ag.c > +++ b/fs/xfs/libxfs/xfs_ag.c > @@ -94,6 +94,68 @@ xfs_perag_put( > trace_xfs_perag_put(pag->pag_mount, pag->pag_agno, ref, > _RET_IP_); > } > > +/* > + * Active references for perag structures. This is for short term > access to the > + * per ag structures for walking trees or accessing state. If an AG > is being > + * shrunk or is offline, then this will fail to find that AG and > return NULL > + * instead. > + */ > +struct xfs_perag * > +xfs_perag_grab( > + struct xfs_mount *mp, > + xfs_agnumber_t agno) > +{ > + struct xfs_perag *pag; > + > + rcu_read_lock(); > + pag = radix_tree_lookup(&mp->m_perag_tree, agno); > + if (pag) { > + trace_xfs_perag_grab(mp, pag->pag_agno, > + atomic_read(&pag->pag_active_ref), > _RET_IP_); > + if (!atomic_inc_not_zero(&pag->pag_active_ref)) > + pag = NULL; > + } > + rcu_read_unlock(); > + return pag; > +} > + > +/* > + * search from @first to find the next perag with the given tag set. > + */ > +struct xfs_perag * > +xfs_perag_grab_tag( > + struct xfs_mount *mp, > + xfs_agnumber_t first, > + int tag) > +{ > + struct xfs_perag *pag; > + int found; > + > + rcu_read_lock(); > + found = radix_tree_gang_lookup_tag(&mp->m_perag_tree, > + (void **)&pag, first, 1, > tag); > + if (found <= 0) { > + rcu_read_unlock(); > + return NULL; > + } > + trace_xfs_perag_grab_tag(mp, pag->pag_agno, > + atomic_read(&pag->pag_active_ref), _RET_IP_); > + if (!atomic_inc_not_zero(&pag->pag_active_ref)) > + pag = NULL; > + rcu_read_unlock(); > + return pag; > +} > + > +void > +xfs_perag_rele( > + struct xfs_perag *pag) > +{ > + trace_xfs_perag_rele(pag->pag_mount, pag->pag_agno, > + atomic_read(&pag->pag_active_ref), _RET_IP_); > + if (atomic_dec_and_test(&pag->pag_active_ref)) > + wake_up(&pag->pag_active_wq); > +} > + > /* > * xfs_initialize_perag_data > * > @@ -196,6 +258,10 @@ xfs_free_perag( > cancel_delayed_work_sync(&pag->pag_blockgc_work); > xfs_buf_hash_destroy(pag); > > + /* drop the mount's active reference */ > + xfs_perag_rele(pag); > + XFS_IS_CORRUPT(pag->pag_mount, > + atomic_read(&pag->pag_active_ref) != > 0); > call_rcu(&pag->rcu_head, __xfs_free_perag); > } > } > @@ -314,6 +380,7 @@ xfs_initialize_perag( > INIT_DELAYED_WORK(&pag->pag_blockgc_work, > xfs_blockgc_worker); > INIT_RADIX_TREE(&pag->pag_ici_root, GFP_ATOMIC); > init_waitqueue_head(&pag->pagb_wait); > + init_waitqueue_head(&pag->pag_active_wq); > pag->pagb_count = 0; > pag->pagb_tree = RB_ROOT; > #endif /* __KERNEL__ */ > @@ -322,6 +389,9 @@ xfs_initialize_perag( > if (error) > goto out_remove_pag; > > + /* Active ref owned by mount indicates AG is online. > */ > + atomic_set(&pag->pag_active_ref, 1); > + > /* first new pag is fully initialized */ > if (first_initialised == NULLAGNUMBER) > first_initialised = index; > diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h > index 191b22b9a35b..aeb21c8df201 100644 > --- a/fs/xfs/libxfs/xfs_ag.h > +++ b/fs/xfs/libxfs/xfs_ag.h > @@ -32,7 +32,9 @@ struct xfs_ag_resv { > struct xfs_perag { > struct xfs_mount *pag_mount; /* owner filesystem */ > xfs_agnumber_t pag_agno; /* AG this structure belongs > to */ > - atomic_t pag_ref; /* perag reference count */ > + atomic_t pag_ref; /* passive reference count */ > + atomic_t pag_active_ref; /* active reference count */ > + wait_queue_head_t pag_active_wq;/* woken active_ref falls to > zero */ > char pagf_init; /* this agf's entry is > initialized */ > char pagi_init; /* this agi's entry is > initialized */ > char pagf_metadata; /* the agf is preferred to be > metadata */ > @@ -111,11 +113,18 @@ int xfs_initialize_perag(struct xfs_mount *mp, > xfs_agnumber_t agcount, > int xfs_initialize_perag_data(struct xfs_mount *mp, xfs_agnumber_t > agno); > void xfs_free_perag(struct xfs_mount *mp); > > +/* Passive AG references */ > struct xfs_perag *xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t > agno); > struct xfs_perag *xfs_perag_get_tag(struct xfs_mount *mp, > xfs_agnumber_t agno, > unsigned int tag); > void xfs_perag_put(struct xfs_perag *pag); > > +/* Active AG references */ > +struct xfs_perag *xfs_perag_grab(struct xfs_mount *, > xfs_agnumber_t); > +struct xfs_perag *xfs_perag_grab_tag(struct xfs_mount *, > xfs_agnumber_t, > + int tag); > +void xfs_perag_rele(struct xfs_perag *pag); > + > /* > * Per-ag geometry infomation and validation > */ > @@ -193,14 +202,18 @@ xfs_perag_next( > struct xfs_mount *mp = pag->pag_mount; > > *agno = pag->pag_agno + 1; > - xfs_perag_put(pag); > - if (*agno > end_agno) > - return NULL; > - return xfs_perag_get(mp, *agno); > + xfs_perag_rele(pag); > + while (*agno <= end_agno) { > + pag = xfs_perag_grab(mp, *agno); > + if (pag) > + return pag; > + (*agno)++; > + } > + return NULL; > } > > #define for_each_perag_range(mp, agno, end_agno, pag) \ > - for ((pag) = xfs_perag_get((mp), (agno)); \ > + for ((pag) = xfs_perag_grab((mp), (agno)); \ > (pag) != NULL; \ > (pag) = xfs_perag_next((pag), &(agno), (end_agno))) > > @@ -213,11 +226,11 @@ xfs_perag_next( > for_each_perag_from((mp), (agno), (pag)) > > #define for_each_perag_tag(mp, agno, pag, tag) \ > - for ((agno) = 0, (pag) = xfs_perag_get_tag((mp), 0, (tag)); \ > + for ((agno) = 0, (pag) = xfs_perag_grab_tag((mp), 0, (tag)); > \ > (pag) != NULL; \ > (agno) = (pag)->pag_agno + 1, \ > - xfs_perag_put(pag), \ > - (pag) = xfs_perag_get_tag((mp), (agno), (tag))) > + xfs_perag_rele(pag), \ > + (pag) = xfs_perag_grab_tag((mp), (agno), (tag))) > > struct aghdr_init_data { > /* per ag data */ > diff --git a/fs/xfs/scrub/bmap.c b/fs/xfs/scrub/bmap.c > index d50d0eab196a..dbbc7037074c 100644 > --- a/fs/xfs/scrub/bmap.c > +++ b/fs/xfs/scrub/bmap.c > @@ -662,7 +662,7 @@ xchk_bmap_check_rmaps( > error = xchk_bmap_check_ag_rmaps(sc, whichfork, pag); > if (error || > (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)) { > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > return error; > } > } > diff --git a/fs/xfs/scrub/fscounters.c b/fs/xfs/scrub/fscounters.c > index 4777e7b89fdc..ef97670970c3 100644 > --- a/fs/xfs/scrub/fscounters.c > +++ b/fs/xfs/scrub/fscounters.c > @@ -117,7 +117,7 @@ xchk_fscount_warmup( > if (agi_bp) > xfs_buf_relse(agi_bp); > if (pag) > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > return error; > } > > @@ -249,7 +249,7 @@ xchk_fscount_aggregate_agcounts( > > } > if (pag) > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > if (error) { > xchk_set_incomplete(sc); > return error; > diff --git a/fs/xfs/xfs_fsmap.c b/fs/xfs/xfs_fsmap.c > index 88a88506ffff..120d284a03fe 100644 > --- a/fs/xfs/xfs_fsmap.c > +++ b/fs/xfs/xfs_fsmap.c > @@ -688,11 +688,11 @@ __xfs_getfsmap_datadev( > info->agf_bp = NULL; > } > if (info->pag) { > - xfs_perag_put(info->pag); > + xfs_perag_rele(info->pag); > info->pag = NULL; > } else if (pag) { > /* loop termination case */ > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > } > > return error; > diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c > index ddeaccc04aec..0f4a014dded3 100644 > --- a/fs/xfs/xfs_icache.c > +++ b/fs/xfs/xfs_icache.c > @@ -1767,7 +1767,7 @@ xfs_icwalk( > if (error) { > last_error = error; > if (error == -EFSCORRUPTED) { > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > break; > } > } > diff --git a/fs/xfs/xfs_iwalk.c b/fs/xfs/xfs_iwalk.c > index 7558486f4937..c31857d903a4 100644 > --- a/fs/xfs/xfs_iwalk.c > +++ b/fs/xfs/xfs_iwalk.c > @@ -591,7 +591,7 @@ xfs_iwalk( > } > > if (iwag.pag) > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > xfs_iwalk_free(&iwag); > return error; > } > @@ -683,7 +683,7 @@ xfs_iwalk_threaded( > break; > } > if (pag) > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > if (polled) > xfs_pwork_poll(&pctl); > return xfs_pwork_destroy(&pctl); > @@ -776,7 +776,7 @@ xfs_inobt_walk( > } > > if (iwag.pag) > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > xfs_iwalk_free(&iwag); > return error; > } > diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c > index 57bf59ff4854..f5dc46ce9803 100644 > --- a/fs/xfs/xfs_reflink.c > +++ b/fs/xfs/xfs_reflink.c > @@ -927,7 +927,7 @@ xfs_reflink_recover_cow( > for_each_perag(mp, agno, pag) { > error = xfs_refcount_recover_cow_leftovers(mp, pag); > if (error) { > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > break; > } > } > diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h > index 7dc57db6aa42..f0b62054ea68 100644 > --- a/fs/xfs/xfs_trace.h > +++ b/fs/xfs/xfs_trace.h > @@ -189,6 +189,9 @@ DEFINE_EVENT(xfs_perag_class, name, \ > DEFINE_PERAG_REF_EVENT(xfs_perag_get); > DEFINE_PERAG_REF_EVENT(xfs_perag_get_tag); > DEFINE_PERAG_REF_EVENT(xfs_perag_put); > +DEFINE_PERAG_REF_EVENT(xfs_perag_grab); > +DEFINE_PERAG_REF_EVENT(xfs_perag_grab_tag); > +DEFINE_PERAG_REF_EVENT(xfs_perag_rele); > DEFINE_PERAG_REF_EVENT(xfs_perag_set_inode_tag); > DEFINE_PERAG_REF_EVENT(xfs_perag_clear_inode_tag); >
On Thu, Jan 19, 2023 at 09:44:30AM +1100, Dave Chinner wrote: > From: Dave Chinner <dchinner@redhat.com> > > We need to be able to dynamically remove instantiated AGs from > memory safely, either for shrinking the filesystem or paging AG > state in and out of memory (e.g. supporting millions of AGs). This > means we need to be able to safely exclude operations from accessing > perags while dynamic removal is in progress. > > To do this, introduce the concept of active and passive references. > Active references are required for high level operations that make > use of an AG for a given operation (e.g. allocation) and pin the > perag in memory for the duration of the operation that is operating > on the perag (e.g. transaction scope). This means we can fail to get > an active reference to an AG, hence callers of the new active > reference API must be able to handle lookup failure gracefully. > > Passive references are used in low level code, where we might need > to access the perag structure for the purposes of completing high > level operations. For example, buffers need to use passive > references because: > - we need to be able to do metadata IO during operations like grow > and shrink transactions where high level active references to the > AG have already been blocked > - buffers need to pin the perag until they are reclaimed from > memory, something that high level code has no direct control over. > - unused cached buffers should not prevent a shrink from being > started. > > Hence we have active references that will form exclusion barriers > for operations to be performed on an AG, and passive references that > will prevent reclaim of the perag until all objects with passive > references have been reclaimed themselves. This is going to be fun to rebase the online fsck series on top of. :) If I'm understanding correctly, active perag refs are for high level code that wants to call down into an AG to do some operation (allocating, freeing, scanning, whatever)? So I think online fsck uniformly wants xfs_perag_grab/rele, right? Passive refs are (I think) for lower level code that's wants to call up into an AG to finish off something that was already started? And probably by upper level code? So the amount of code that actually wants a passive reference is pretty small? > This patch introduce xfs_perag_grab()/xfs_perag_rele() as the API > for active AG reference functionality. We also need to convert the > for_each_perag*() iterators to use active references, which will > start the process of converting high level code over to using active > references. Conversion of non-iterator based code to active > references will be done in followup patches. Is there any code that iterates perag structures via passive references? I think the answer to this is 'no'? The code changes look all right. If the answers to the above questions are "yes", "yes", "yes", and "no", then: Reviewed-by: Darrick J. Wong <djwong@kernel.org> --D > Note that the implementation using reference counting is really just > a development vehicle for the API to ensure we don't have any leaks > in the callers. Once we need to remove perag structures from memory > dyanmically, we will need a much more robust per-ag state transition > mechanism for preventing new references from being taken while we > wait for existing references to drain before removal from memory can > occur.... > > Signed-off-by: Dave Chinner <dchinner@redhat.com> > --- > fs/xfs/libxfs/xfs_ag.c | 70 +++++++++++++++++++++++++++++++++++++++ > fs/xfs/libxfs/xfs_ag.h | 31 ++++++++++++----- > fs/xfs/scrub/bmap.c | 2 +- > fs/xfs/scrub/fscounters.c | 4 +-- > fs/xfs/xfs_fsmap.c | 4 +-- > fs/xfs/xfs_icache.c | 2 +- > fs/xfs/xfs_iwalk.c | 6 ++-- > fs/xfs/xfs_reflink.c | 2 +- > fs/xfs/xfs_trace.h | 3 ++ > 9 files changed, 105 insertions(+), 19 deletions(-) > > diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c > index bb0c700afe3c..46e25c682bf4 100644 > --- a/fs/xfs/libxfs/xfs_ag.c > +++ b/fs/xfs/libxfs/xfs_ag.c > @@ -94,6 +94,68 @@ xfs_perag_put( > trace_xfs_perag_put(pag->pag_mount, pag->pag_agno, ref, _RET_IP_); > } > > +/* > + * Active references for perag structures. This is for short term access to the > + * per ag structures for walking trees or accessing state. If an AG is being > + * shrunk or is offline, then this will fail to find that AG and return NULL > + * instead. > + */ > +struct xfs_perag * > +xfs_perag_grab( > + struct xfs_mount *mp, > + xfs_agnumber_t agno) > +{ > + struct xfs_perag *pag; > + > + rcu_read_lock(); > + pag = radix_tree_lookup(&mp->m_perag_tree, agno); > + if (pag) { > + trace_xfs_perag_grab(mp, pag->pag_agno, > + atomic_read(&pag->pag_active_ref), _RET_IP_); > + if (!atomic_inc_not_zero(&pag->pag_active_ref)) > + pag = NULL; > + } > + rcu_read_unlock(); > + return pag; > +} > + > +/* > + * search from @first to find the next perag with the given tag set. > + */ > +struct xfs_perag * > +xfs_perag_grab_tag( > + struct xfs_mount *mp, > + xfs_agnumber_t first, > + int tag) > +{ > + struct xfs_perag *pag; > + int found; > + > + rcu_read_lock(); > + found = radix_tree_gang_lookup_tag(&mp->m_perag_tree, > + (void **)&pag, first, 1, tag); > + if (found <= 0) { > + rcu_read_unlock(); > + return NULL; > + } > + trace_xfs_perag_grab_tag(mp, pag->pag_agno, > + atomic_read(&pag->pag_active_ref), _RET_IP_); > + if (!atomic_inc_not_zero(&pag->pag_active_ref)) > + pag = NULL; > + rcu_read_unlock(); > + return pag; > +} > + > +void > +xfs_perag_rele( > + struct xfs_perag *pag) > +{ > + trace_xfs_perag_rele(pag->pag_mount, pag->pag_agno, > + atomic_read(&pag->pag_active_ref), _RET_IP_); > + if (atomic_dec_and_test(&pag->pag_active_ref)) > + wake_up(&pag->pag_active_wq); > +} > + > /* > * xfs_initialize_perag_data > * > @@ -196,6 +258,10 @@ xfs_free_perag( > cancel_delayed_work_sync(&pag->pag_blockgc_work); > xfs_buf_hash_destroy(pag); > > + /* drop the mount's active reference */ > + xfs_perag_rele(pag); > + XFS_IS_CORRUPT(pag->pag_mount, > + atomic_read(&pag->pag_active_ref) != 0); > call_rcu(&pag->rcu_head, __xfs_free_perag); > } > } > @@ -314,6 +380,7 @@ xfs_initialize_perag( > INIT_DELAYED_WORK(&pag->pag_blockgc_work, xfs_blockgc_worker); > INIT_RADIX_TREE(&pag->pag_ici_root, GFP_ATOMIC); > init_waitqueue_head(&pag->pagb_wait); > + init_waitqueue_head(&pag->pag_active_wq); > pag->pagb_count = 0; > pag->pagb_tree = RB_ROOT; > #endif /* __KERNEL__ */ > @@ -322,6 +389,9 @@ xfs_initialize_perag( > if (error) > goto out_remove_pag; > > + /* Active ref owned by mount indicates AG is online. */ > + atomic_set(&pag->pag_active_ref, 1); > + > /* first new pag is fully initialized */ > if (first_initialised == NULLAGNUMBER) > first_initialised = index; > diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h > index 191b22b9a35b..aeb21c8df201 100644 > --- a/fs/xfs/libxfs/xfs_ag.h > +++ b/fs/xfs/libxfs/xfs_ag.h > @@ -32,7 +32,9 @@ struct xfs_ag_resv { > struct xfs_perag { > struct xfs_mount *pag_mount; /* owner filesystem */ > xfs_agnumber_t pag_agno; /* AG this structure belongs to */ > - atomic_t pag_ref; /* perag reference count */ > + atomic_t pag_ref; /* passive reference count */ > + atomic_t pag_active_ref; /* active reference count */ > + wait_queue_head_t pag_active_wq;/* woken active_ref falls to zero */ > char pagf_init; /* this agf's entry is initialized */ > char pagi_init; /* this agi's entry is initialized */ > char pagf_metadata; /* the agf is preferred to be metadata */ > @@ -111,11 +113,18 @@ int xfs_initialize_perag(struct xfs_mount *mp, xfs_agnumber_t agcount, > int xfs_initialize_perag_data(struct xfs_mount *mp, xfs_agnumber_t agno); > void xfs_free_perag(struct xfs_mount *mp); > > +/* Passive AG references */ > struct xfs_perag *xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t agno); > struct xfs_perag *xfs_perag_get_tag(struct xfs_mount *mp, xfs_agnumber_t agno, > unsigned int tag); > void xfs_perag_put(struct xfs_perag *pag); > > +/* Active AG references */ > +struct xfs_perag *xfs_perag_grab(struct xfs_mount *, xfs_agnumber_t); > +struct xfs_perag *xfs_perag_grab_tag(struct xfs_mount *, xfs_agnumber_t, > + int tag); > +void xfs_perag_rele(struct xfs_perag *pag); > + > /* > * Per-ag geometry infomation and validation > */ > @@ -193,14 +202,18 @@ xfs_perag_next( > struct xfs_mount *mp = pag->pag_mount; > > *agno = pag->pag_agno + 1; > - xfs_perag_put(pag); > - if (*agno > end_agno) > - return NULL; > - return xfs_perag_get(mp, *agno); > + xfs_perag_rele(pag); > + while (*agno <= end_agno) { > + pag = xfs_perag_grab(mp, *agno); > + if (pag) > + return pag; > + (*agno)++; > + } > + return NULL; > } > > #define for_each_perag_range(mp, agno, end_agno, pag) \ > - for ((pag) = xfs_perag_get((mp), (agno)); \ > + for ((pag) = xfs_perag_grab((mp), (agno)); \ > (pag) != NULL; \ > (pag) = xfs_perag_next((pag), &(agno), (end_agno))) > > @@ -213,11 +226,11 @@ xfs_perag_next( > for_each_perag_from((mp), (agno), (pag)) > > #define for_each_perag_tag(mp, agno, pag, tag) \ > - for ((agno) = 0, (pag) = xfs_perag_get_tag((mp), 0, (tag)); \ > + for ((agno) = 0, (pag) = xfs_perag_grab_tag((mp), 0, (tag)); \ > (pag) != NULL; \ > (agno) = (pag)->pag_agno + 1, \ > - xfs_perag_put(pag), \ > - (pag) = xfs_perag_get_tag((mp), (agno), (tag))) > + xfs_perag_rele(pag), \ > + (pag) = xfs_perag_grab_tag((mp), (agno), (tag))) > > struct aghdr_init_data { > /* per ag data */ > diff --git a/fs/xfs/scrub/bmap.c b/fs/xfs/scrub/bmap.c > index d50d0eab196a..dbbc7037074c 100644 > --- a/fs/xfs/scrub/bmap.c > +++ b/fs/xfs/scrub/bmap.c > @@ -662,7 +662,7 @@ xchk_bmap_check_rmaps( > error = xchk_bmap_check_ag_rmaps(sc, whichfork, pag); > if (error || > (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)) { > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > return error; > } > } > diff --git a/fs/xfs/scrub/fscounters.c b/fs/xfs/scrub/fscounters.c > index 4777e7b89fdc..ef97670970c3 100644 > --- a/fs/xfs/scrub/fscounters.c > +++ b/fs/xfs/scrub/fscounters.c > @@ -117,7 +117,7 @@ xchk_fscount_warmup( > if (agi_bp) > xfs_buf_relse(agi_bp); > if (pag) > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > return error; > } > > @@ -249,7 +249,7 @@ xchk_fscount_aggregate_agcounts( > > } > if (pag) > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > if (error) { > xchk_set_incomplete(sc); > return error; > diff --git a/fs/xfs/xfs_fsmap.c b/fs/xfs/xfs_fsmap.c > index 88a88506ffff..120d284a03fe 100644 > --- a/fs/xfs/xfs_fsmap.c > +++ b/fs/xfs/xfs_fsmap.c > @@ -688,11 +688,11 @@ __xfs_getfsmap_datadev( > info->agf_bp = NULL; > } > if (info->pag) { > - xfs_perag_put(info->pag); > + xfs_perag_rele(info->pag); > info->pag = NULL; > } else if (pag) { > /* loop termination case */ > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > } > > return error; > diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c > index ddeaccc04aec..0f4a014dded3 100644 > --- a/fs/xfs/xfs_icache.c > +++ b/fs/xfs/xfs_icache.c > @@ -1767,7 +1767,7 @@ xfs_icwalk( > if (error) { > last_error = error; > if (error == -EFSCORRUPTED) { > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > break; > } > } > diff --git a/fs/xfs/xfs_iwalk.c b/fs/xfs/xfs_iwalk.c > index 7558486f4937..c31857d903a4 100644 > --- a/fs/xfs/xfs_iwalk.c > +++ b/fs/xfs/xfs_iwalk.c > @@ -591,7 +591,7 @@ xfs_iwalk( > } > > if (iwag.pag) > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > xfs_iwalk_free(&iwag); > return error; > } > @@ -683,7 +683,7 @@ xfs_iwalk_threaded( > break; > } > if (pag) > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > if (polled) > xfs_pwork_poll(&pctl); > return xfs_pwork_destroy(&pctl); > @@ -776,7 +776,7 @@ xfs_inobt_walk( > } > > if (iwag.pag) > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > xfs_iwalk_free(&iwag); > return error; > } > diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c > index 57bf59ff4854..f5dc46ce9803 100644 > --- a/fs/xfs/xfs_reflink.c > +++ b/fs/xfs/xfs_reflink.c > @@ -927,7 +927,7 @@ xfs_reflink_recover_cow( > for_each_perag(mp, agno, pag) { > error = xfs_refcount_recover_cow_leftovers(mp, pag); > if (error) { > - xfs_perag_put(pag); > + xfs_perag_rele(pag); > break; > } > } > diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h > index 7dc57db6aa42..f0b62054ea68 100644 > --- a/fs/xfs/xfs_trace.h > +++ b/fs/xfs/xfs_trace.h > @@ -189,6 +189,9 @@ DEFINE_EVENT(xfs_perag_class, name, \ > DEFINE_PERAG_REF_EVENT(xfs_perag_get); > DEFINE_PERAG_REF_EVENT(xfs_perag_get_tag); > DEFINE_PERAG_REF_EVENT(xfs_perag_put); > +DEFINE_PERAG_REF_EVENT(xfs_perag_grab); > +DEFINE_PERAG_REF_EVENT(xfs_perag_grab_tag); > +DEFINE_PERAG_REF_EVENT(xfs_perag_rele); > DEFINE_PERAG_REF_EVENT(xfs_perag_set_inode_tag); > DEFINE_PERAG_REF_EVENT(xfs_perag_clear_inode_tag); > > -- > 2.39.0 >
On Wed, Feb 01, 2023 at 11:08:53AM -0800, Darrick J. Wong wrote: > On Thu, Jan 19, 2023 at 09:44:30AM +1100, Dave Chinner wrote: > > From: Dave Chinner <dchinner@redhat.com> > > > > We need to be able to dynamically remove instantiated AGs from > > memory safely, either for shrinking the filesystem or paging AG > > state in and out of memory (e.g. supporting millions of AGs). This > > means we need to be able to safely exclude operations from accessing > > perags while dynamic removal is in progress. > > > > To do this, introduce the concept of active and passive references. > > Active references are required for high level operations that make > > use of an AG for a given operation (e.g. allocation) and pin the > > perag in memory for the duration of the operation that is operating > > on the perag (e.g. transaction scope). This means we can fail to get > > an active reference to an AG, hence callers of the new active > > reference API must be able to handle lookup failure gracefully. > > > > Passive references are used in low level code, where we might need > > to access the perag structure for the purposes of completing high > > level operations. For example, buffers need to use passive > > references because: > > - we need to be able to do metadata IO during operations like grow > > and shrink transactions where high level active references to the > > AG have already been blocked > > - buffers need to pin the perag until they are reclaimed from > > memory, something that high level code has no direct control over. > > - unused cached buffers should not prevent a shrink from being > > started. > > > > Hence we have active references that will form exclusion barriers > > for operations to be performed on an AG, and passive references that > > will prevent reclaim of the perag until all objects with passive > > references have been reclaimed themselves. > > This is going to be fun to rebase the online fsck series on top of. :) > > If I'm understanding correctly, active perag refs are for high level > code that wants to call down into an AG to do some operation > (allocating, freeing, scanning, whatever)? So I think online fsck > uniformly wants xfs_perag_grab/rele, right? That depends. For scrubbing, yes, active references are probably going to be needed. For repair of AG structures where the AG needs to be taken offline, we will likely have to take the AG offline to prevent allocation from being attempted in them. Yes, we currently use the AGF/AGI lock to prevent that, but this results in blocking user applications during allocation until repair is done with the AG. We really want application allocation to naturally skip AGs under repair, not block until the repair is done.... As such, I think the answer is scrub should use active references as it scans, but repair needs to use passive references once the AG has had it's state changed to "offline" as active references will only be available on "fully online" AGs. > Passive refs are (I think) for lower level code that's wants to call up > into an AG to finish off something that was already started? Yes, like buffers carrying a passive reference to pin the perag while there are cached buffers indexed by the perag buffer hash. Here we only care about the existence of the perag structure, as we need to do IO to the AG metadata regardless of whether the perag is active or not. > And > probably by upper level code? So the amount of code that actually wants > a passive reference is pretty small? I don't think it's "small" - all the back end code that uses the perag as the root of indexing structures will likely need passive references. The mental model I'm using is that active references are for tracking user-facing and user-data operations that require perag access. That's things like inode allocation, data extent allocation, etc which will need to skip over AGs that aren't available for storing new user data/metadata at the current time. Anything that is internal (e.g. metadata buffers, inode cache walks for reclaim) that needs to run regardless of user operation just needs an existence guarantee over the life of the object. This is what passive references provide - the perag cannot be freed from memory while there are still passive references to it. Hence I'm looking at active references as a mechanism that can provide an access barrier/drain for serialising per-ag operational state changes, not to provide per-ag existence guarantees. Passive references provide low level existence guarantees, active references allow online/offline/no-alloc/shrinking/etc operational state changes to be made safely. > > This patch introduce xfs_perag_grab()/xfs_perag_rele() as the API > > for active AG reference functionality. We also need to convert the > > for_each_perag*() iterators to use active references, which will > > start the process of converting high level code over to using active > > references. Conversion of non-iterator based code to active > > references will be done in followup patches. > > Is there any code that iterates perag structures via passive references? > I think the answer to this is 'no'? I think the answer is yes - inode cache walking is a good example of this. That will (eventually) have to grab a passive reference to the perag and check the return - if it fails the perag has just been torn down so we need to skip it. If it succeeds then we have a reference that pins the perag in memory and we can safely walk the inode cache structures in that perag. Some of the operations that the inode cache walks perform (e.g. block trimming) might need active references to per-ags to perform their work (e.g. because a different AG is offline being repaired and so we cannot free the post-eof blocks without blocking on that offline AG). However, we don't want to skip inode cache walks just because an AG is not allowing new allocations to be made in it.... > The code changes look all right. If the answers to the above questions > are "yes", "yes", "yes", and "no", then: > Reviewed-by: Darrick J. Wong <djwong@kernel.org> The answers are a whole lot more nuanced than that, unfortunately. Which means that some of the repair infrastructure will need to be done differently as the state changes for shrink are introduced. I don't think there's any show-stoppers here, though. Cheers, Dave.
diff --git a/fs/xfs/libxfs/xfs_ag.c b/fs/xfs/libxfs/xfs_ag.c index bb0c700afe3c..46e25c682bf4 100644 --- a/fs/xfs/libxfs/xfs_ag.c +++ b/fs/xfs/libxfs/xfs_ag.c @@ -94,6 +94,68 @@ xfs_perag_put( trace_xfs_perag_put(pag->pag_mount, pag->pag_agno, ref, _RET_IP_); } +/* + * Active references for perag structures. This is for short term access to the + * per ag structures for walking trees or accessing state. If an AG is being + * shrunk or is offline, then this will fail to find that AG and return NULL + * instead. + */ +struct xfs_perag * +xfs_perag_grab( + struct xfs_mount *mp, + xfs_agnumber_t agno) +{ + struct xfs_perag *pag; + + rcu_read_lock(); + pag = radix_tree_lookup(&mp->m_perag_tree, agno); + if (pag) { + trace_xfs_perag_grab(mp, pag->pag_agno, + atomic_read(&pag->pag_active_ref), _RET_IP_); + if (!atomic_inc_not_zero(&pag->pag_active_ref)) + pag = NULL; + } + rcu_read_unlock(); + return pag; +} + +/* + * search from @first to find the next perag with the given tag set. + */ +struct xfs_perag * +xfs_perag_grab_tag( + struct xfs_mount *mp, + xfs_agnumber_t first, + int tag) +{ + struct xfs_perag *pag; + int found; + + rcu_read_lock(); + found = radix_tree_gang_lookup_tag(&mp->m_perag_tree, + (void **)&pag, first, 1, tag); + if (found <= 0) { + rcu_read_unlock(); + return NULL; + } + trace_xfs_perag_grab_tag(mp, pag->pag_agno, + atomic_read(&pag->pag_active_ref), _RET_IP_); + if (!atomic_inc_not_zero(&pag->pag_active_ref)) + pag = NULL; + rcu_read_unlock(); + return pag; +} + +void +xfs_perag_rele( + struct xfs_perag *pag) +{ + trace_xfs_perag_rele(pag->pag_mount, pag->pag_agno, + atomic_read(&pag->pag_active_ref), _RET_IP_); + if (atomic_dec_and_test(&pag->pag_active_ref)) + wake_up(&pag->pag_active_wq); +} + /* * xfs_initialize_perag_data * @@ -196,6 +258,10 @@ xfs_free_perag( cancel_delayed_work_sync(&pag->pag_blockgc_work); xfs_buf_hash_destroy(pag); + /* drop the mount's active reference */ + xfs_perag_rele(pag); + XFS_IS_CORRUPT(pag->pag_mount, + atomic_read(&pag->pag_active_ref) != 0); call_rcu(&pag->rcu_head, __xfs_free_perag); } } @@ -314,6 +380,7 @@ xfs_initialize_perag( INIT_DELAYED_WORK(&pag->pag_blockgc_work, xfs_blockgc_worker); INIT_RADIX_TREE(&pag->pag_ici_root, GFP_ATOMIC); init_waitqueue_head(&pag->pagb_wait); + init_waitqueue_head(&pag->pag_active_wq); pag->pagb_count = 0; pag->pagb_tree = RB_ROOT; #endif /* __KERNEL__ */ @@ -322,6 +389,9 @@ xfs_initialize_perag( if (error) goto out_remove_pag; + /* Active ref owned by mount indicates AG is online. */ + atomic_set(&pag->pag_active_ref, 1); + /* first new pag is fully initialized */ if (first_initialised == NULLAGNUMBER) first_initialised = index; diff --git a/fs/xfs/libxfs/xfs_ag.h b/fs/xfs/libxfs/xfs_ag.h index 191b22b9a35b..aeb21c8df201 100644 --- a/fs/xfs/libxfs/xfs_ag.h +++ b/fs/xfs/libxfs/xfs_ag.h @@ -32,7 +32,9 @@ struct xfs_ag_resv { struct xfs_perag { struct xfs_mount *pag_mount; /* owner filesystem */ xfs_agnumber_t pag_agno; /* AG this structure belongs to */ - atomic_t pag_ref; /* perag reference count */ + atomic_t pag_ref; /* passive reference count */ + atomic_t pag_active_ref; /* active reference count */ + wait_queue_head_t pag_active_wq;/* woken active_ref falls to zero */ char pagf_init; /* this agf's entry is initialized */ char pagi_init; /* this agi's entry is initialized */ char pagf_metadata; /* the agf is preferred to be metadata */ @@ -111,11 +113,18 @@ int xfs_initialize_perag(struct xfs_mount *mp, xfs_agnumber_t agcount, int xfs_initialize_perag_data(struct xfs_mount *mp, xfs_agnumber_t agno); void xfs_free_perag(struct xfs_mount *mp); +/* Passive AG references */ struct xfs_perag *xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t agno); struct xfs_perag *xfs_perag_get_tag(struct xfs_mount *mp, xfs_agnumber_t agno, unsigned int tag); void xfs_perag_put(struct xfs_perag *pag); +/* Active AG references */ +struct xfs_perag *xfs_perag_grab(struct xfs_mount *, xfs_agnumber_t); +struct xfs_perag *xfs_perag_grab_tag(struct xfs_mount *, xfs_agnumber_t, + int tag); +void xfs_perag_rele(struct xfs_perag *pag); + /* * Per-ag geometry infomation and validation */ @@ -193,14 +202,18 @@ xfs_perag_next( struct xfs_mount *mp = pag->pag_mount; *agno = pag->pag_agno + 1; - xfs_perag_put(pag); - if (*agno > end_agno) - return NULL; - return xfs_perag_get(mp, *agno); + xfs_perag_rele(pag); + while (*agno <= end_agno) { + pag = xfs_perag_grab(mp, *agno); + if (pag) + return pag; + (*agno)++; + } + return NULL; } #define for_each_perag_range(mp, agno, end_agno, pag) \ - for ((pag) = xfs_perag_get((mp), (agno)); \ + for ((pag) = xfs_perag_grab((mp), (agno)); \ (pag) != NULL; \ (pag) = xfs_perag_next((pag), &(agno), (end_agno))) @@ -213,11 +226,11 @@ xfs_perag_next( for_each_perag_from((mp), (agno), (pag)) #define for_each_perag_tag(mp, agno, pag, tag) \ - for ((agno) = 0, (pag) = xfs_perag_get_tag((mp), 0, (tag)); \ + for ((agno) = 0, (pag) = xfs_perag_grab_tag((mp), 0, (tag)); \ (pag) != NULL; \ (agno) = (pag)->pag_agno + 1, \ - xfs_perag_put(pag), \ - (pag) = xfs_perag_get_tag((mp), (agno), (tag))) + xfs_perag_rele(pag), \ + (pag) = xfs_perag_grab_tag((mp), (agno), (tag))) struct aghdr_init_data { /* per ag data */ diff --git a/fs/xfs/scrub/bmap.c b/fs/xfs/scrub/bmap.c index d50d0eab196a..dbbc7037074c 100644 --- a/fs/xfs/scrub/bmap.c +++ b/fs/xfs/scrub/bmap.c @@ -662,7 +662,7 @@ xchk_bmap_check_rmaps( error = xchk_bmap_check_ag_rmaps(sc, whichfork, pag); if (error || (sc->sm->sm_flags & XFS_SCRUB_OFLAG_CORRUPT)) { - xfs_perag_put(pag); + xfs_perag_rele(pag); return error; } } diff --git a/fs/xfs/scrub/fscounters.c b/fs/xfs/scrub/fscounters.c index 4777e7b89fdc..ef97670970c3 100644 --- a/fs/xfs/scrub/fscounters.c +++ b/fs/xfs/scrub/fscounters.c @@ -117,7 +117,7 @@ xchk_fscount_warmup( if (agi_bp) xfs_buf_relse(agi_bp); if (pag) - xfs_perag_put(pag); + xfs_perag_rele(pag); return error; } @@ -249,7 +249,7 @@ xchk_fscount_aggregate_agcounts( } if (pag) - xfs_perag_put(pag); + xfs_perag_rele(pag); if (error) { xchk_set_incomplete(sc); return error; diff --git a/fs/xfs/xfs_fsmap.c b/fs/xfs/xfs_fsmap.c index 88a88506ffff..120d284a03fe 100644 --- a/fs/xfs/xfs_fsmap.c +++ b/fs/xfs/xfs_fsmap.c @@ -688,11 +688,11 @@ __xfs_getfsmap_datadev( info->agf_bp = NULL; } if (info->pag) { - xfs_perag_put(info->pag); + xfs_perag_rele(info->pag); info->pag = NULL; } else if (pag) { /* loop termination case */ - xfs_perag_put(pag); + xfs_perag_rele(pag); } return error; diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c index ddeaccc04aec..0f4a014dded3 100644 --- a/fs/xfs/xfs_icache.c +++ b/fs/xfs/xfs_icache.c @@ -1767,7 +1767,7 @@ xfs_icwalk( if (error) { last_error = error; if (error == -EFSCORRUPTED) { - xfs_perag_put(pag); + xfs_perag_rele(pag); break; } } diff --git a/fs/xfs/xfs_iwalk.c b/fs/xfs/xfs_iwalk.c index 7558486f4937..c31857d903a4 100644 --- a/fs/xfs/xfs_iwalk.c +++ b/fs/xfs/xfs_iwalk.c @@ -591,7 +591,7 @@ xfs_iwalk( } if (iwag.pag) - xfs_perag_put(pag); + xfs_perag_rele(pag); xfs_iwalk_free(&iwag); return error; } @@ -683,7 +683,7 @@ xfs_iwalk_threaded( break; } if (pag) - xfs_perag_put(pag); + xfs_perag_rele(pag); if (polled) xfs_pwork_poll(&pctl); return xfs_pwork_destroy(&pctl); @@ -776,7 +776,7 @@ xfs_inobt_walk( } if (iwag.pag) - xfs_perag_put(pag); + xfs_perag_rele(pag); xfs_iwalk_free(&iwag); return error; } diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c index 57bf59ff4854..f5dc46ce9803 100644 --- a/fs/xfs/xfs_reflink.c +++ b/fs/xfs/xfs_reflink.c @@ -927,7 +927,7 @@ xfs_reflink_recover_cow( for_each_perag(mp, agno, pag) { error = xfs_refcount_recover_cow_leftovers(mp, pag); if (error) { - xfs_perag_put(pag); + xfs_perag_rele(pag); break; } } diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h index 7dc57db6aa42..f0b62054ea68 100644 --- a/fs/xfs/xfs_trace.h +++ b/fs/xfs/xfs_trace.h @@ -189,6 +189,9 @@ DEFINE_EVENT(xfs_perag_class, name, \ DEFINE_PERAG_REF_EVENT(xfs_perag_get); DEFINE_PERAG_REF_EVENT(xfs_perag_get_tag); DEFINE_PERAG_REF_EVENT(xfs_perag_put); +DEFINE_PERAG_REF_EVENT(xfs_perag_grab); +DEFINE_PERAG_REF_EVENT(xfs_perag_grab_tag); +DEFINE_PERAG_REF_EVENT(xfs_perag_rele); DEFINE_PERAG_REF_EVENT(xfs_perag_set_inode_tag); DEFINE_PERAG_REF_EVENT(xfs_perag_clear_inode_tag);