| Message ID | 20201217011157.92549-2-laoar.shao@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | xfs: avoid transaction reservation recursion | expand |
On Thu, Dec 17, 2020 at 09:11:54AM +0800, Yafang Shao wrote: > From: "Matthew Wilcox (Oracle)" <willy@infradead.org> > > Since XFS needs to pretend to be kswapd in some of its worker threads, > create methods to save & restore kswapd state. Don't bother restoring > kswapd state in kswapd -- the only time we reach this code is when we're > exiting and the task_struct is about to be destroyed anyway. > > Cc: Dave Chinner <david@fromorbit.com> > Acked-by: Michal Hocko <mhocko@suse.com> > Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> > Reviewed-by: Christoph Hellwig <hch@lst.de> > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com> > --- > fs/xfs/libxfs/xfs_btree.c | 14 ++++++++------ > include/linux/sched/mm.h | 23 +++++++++++++++++++++++ > mm/vmscan.c | 16 +--------------- > 3 files changed, 32 insertions(+), 21 deletions(-) > > diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c > index 51dbff9b0908..0f35b7a38e76 100644 > --- a/fs/xfs/libxfs/xfs_btree.c > +++ b/fs/xfs/libxfs/xfs_btree.c > @@ -2813,8 +2813,9 @@ xfs_btree_split_worker( > { > struct xfs_btree_split_args *args = container_of(work, > struct xfs_btree_split_args, work); > + bool is_kswapd = args->kswapd; > unsigned long pflags; > - unsigned long new_pflags = PF_MEMALLOC_NOFS; > + int memalloc_nofs; > > /* > * we are in a transaction context here, but may also be doing work > @@ -2822,16 +2823,17 @@ xfs_btree_split_worker( > * temporarily to ensure that we don't block waiting for memory reclaim > * in any way. > */ > - if (args->kswapd) > - new_pflags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; > - > - current_set_flags_nested(&pflags, new_pflags); > + if (is_kswapd) > + pflags = become_kswapd(); > + memalloc_nofs = memalloc_nofs_save(); > > args->result = __xfs_btree_split(args->cur, args->level, args->ptrp, > args->key, args->curp, args->stat); > complete(args->done); > > - current_restore_flags_nested(&pflags, new_pflags); > + memalloc_nofs_restore(memalloc_nofs); > + if (is_kswapd) > + restore_kswapd(pflags); > } > > /* > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h > index d5ece7a9a403..2faf03e79a1e 100644 > --- a/include/linux/sched/mm.h > +++ b/include/linux/sched/mm.h > @@ -278,6 +278,29 @@ static inline void memalloc_nocma_restore(unsigned int flags) > } > #endif > > +/* > + * Tell the memory management code that this thread is working on behalf > + * of background memory reclaim (like kswapd). That means that it will > + * get access to memory reserves should it need to allocate memory in > + * order to make forward progress. With this great power comes great > + * responsibility to not exhaust those reserves. > + */ > +#define KSWAPD_PF_FLAGS (PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD) > + > +static inline unsigned long become_kswapd(void) > +{ > + unsigned long flags = current->flags & KSWAPD_PF_FLAGS; > + > + current->flags |= KSWAPD_PF_FLAGS; > + > + return flags; > +} You can get rid of the empty lines out of this function. > +static inline void restore_kswapd(unsigned long flags) > +{ > + current->flags &= ~(flags ^ KSWAPD_PF_FLAGS); > +} Urk, that requires thinking about to determine whether it is correct. And it is 3 runtime logic operations (^, ~ and &) too. The way all the memalloc_*_restore() functions restore the previous flags is obviously correct and only requires 2 runtime logic operations because the compiler calculates the ~ operation on the constant. So why do it differently here? i.e.: current->flags = (current->flags & ~KSWAPD_PF_FLAGS) | flags; > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3870,19 +3870,7 @@ static int kswapd(void *p) > if (!cpumask_empty(cpumask)) > set_cpus_allowed_ptr(tsk, cpumask); > > - /* > - * Tell the memory management that we're a "memory allocator", > - * and that if we need more memory we should get access to it > - * regardless (see "__alloc_pages()"). "kswapd" should > - * never get caught in the normal page freeing logic. > - * > - * (Kswapd normally doesn't need memory anyway, but sometimes > - * you need a small amount of memory in order to be able to > - * page out something else, and this flag essentially protects > - * us from recursively trying to free more memory as we're > - * trying to free the first piece of memory in the first place). > - */ > - tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; > + become_kswapd(); > set_freezable(); > > WRITE_ONCE(pgdat->kswapd_order, 0); > @@ -3932,8 +3920,6 @@ static int kswapd(void *p) > goto kswapd_try_sleep; > } > > - tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD); > - Missing a restore_kswapd()? Cheers, Dave.
On Thu, Dec 17, 2020 at 02:06:09PM +1100, Dave Chinner wrote: > On Thu, Dec 17, 2020 at 09:11:54AM +0800, Yafang Shao wrote: > > From: "Matthew Wilcox (Oracle)" <willy@infradead.org> > > > > Since XFS needs to pretend to be kswapd in some of its worker threads, > > create methods to save & restore kswapd state. Don't bother restoring > > kswapd state in kswapd -- the only time we reach this code is when we're > > exiting and the task_struct is about to be destroyed anyway. ... > > @@ -3932,8 +3920,6 @@ static int kswapd(void *p) > > goto kswapd_try_sleep; > > } > > > > - tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD); > > - > > Missing a restore_kswapd()? Deliberately.
On Thu, Dec 17, 2020 at 11:06 AM Dave Chinner <david@fromorbit.com> wrote: > > On Thu, Dec 17, 2020 at 09:11:54AM +0800, Yafang Shao wrote: > > From: "Matthew Wilcox (Oracle)" <willy@infradead.org> > > > > Since XFS needs to pretend to be kswapd in some of its worker threads, > > create methods to save & restore kswapd state. Don't bother restoring > > kswapd state in kswapd -- the only time we reach this code is when we're > > exiting and the task_struct is about to be destroyed anyway. > > > > Cc: Dave Chinner <david@fromorbit.com> > > Acked-by: Michal Hocko <mhocko@suse.com> > > Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> > > Reviewed-by: Christoph Hellwig <hch@lst.de> > > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org> > > Signed-off-by: Yafang Shao <laoar.shao@gmail.com> > > --- > > fs/xfs/libxfs/xfs_btree.c | 14 ++++++++------ > > include/linux/sched/mm.h | 23 +++++++++++++++++++++++ > > mm/vmscan.c | 16 +--------------- > > 3 files changed, 32 insertions(+), 21 deletions(-) > > > > diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c > > index 51dbff9b0908..0f35b7a38e76 100644 > > --- a/fs/xfs/libxfs/xfs_btree.c > > +++ b/fs/xfs/libxfs/xfs_btree.c > > @@ -2813,8 +2813,9 @@ xfs_btree_split_worker( > > { > > struct xfs_btree_split_args *args = container_of(work, > > struct xfs_btree_split_args, work); > > + bool is_kswapd = args->kswapd; > > unsigned long pflags; > > - unsigned long new_pflags = PF_MEMALLOC_NOFS; > > + int memalloc_nofs; > > > > /* > > * we are in a transaction context here, but may also be doing work > > @@ -2822,16 +2823,17 @@ xfs_btree_split_worker( > > * temporarily to ensure that we don't block waiting for memory reclaim > > * in any way. > > */ > > - if (args->kswapd) > > - new_pflags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; > > - > > - current_set_flags_nested(&pflags, new_pflags); > > + if (is_kswapd) > > + pflags = become_kswapd(); > > + memalloc_nofs = memalloc_nofs_save(); > > > > args->result = __xfs_btree_split(args->cur, args->level, args->ptrp, > > args->key, args->curp, args->stat); > > complete(args->done); > > > > - current_restore_flags_nested(&pflags, new_pflags); > > + memalloc_nofs_restore(memalloc_nofs); > > + if (is_kswapd) > > + restore_kswapd(pflags); > > } > > > > /* > > diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h > > index d5ece7a9a403..2faf03e79a1e 100644 > > --- a/include/linux/sched/mm.h > > +++ b/include/linux/sched/mm.h > > @@ -278,6 +278,29 @@ static inline void memalloc_nocma_restore(unsigned int flags) > > } > > #endif > > > > +/* > > + * Tell the memory management code that this thread is working on behalf > > + * of background memory reclaim (like kswapd). That means that it will > > + * get access to memory reserves should it need to allocate memory in > > + * order to make forward progress. With this great power comes great > > + * responsibility to not exhaust those reserves. > > + */ > > +#define KSWAPD_PF_FLAGS (PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD) > > + > > +static inline unsigned long become_kswapd(void) > > +{ > > + unsigned long flags = current->flags & KSWAPD_PF_FLAGS; > > + > > + current->flags |= KSWAPD_PF_FLAGS; > > + > > + return flags; > > +} > > You can get rid of the empty lines out of this function. > > > +static inline void restore_kswapd(unsigned long flags) > > +{ > > + current->flags &= ~(flags ^ KSWAPD_PF_FLAGS); > > +} > > Urk, that requires thinking about to determine whether it is > correct. And it is 3 runtime logic operations (^, ~ and &) too. The > way all the memalloc_*_restore() functions restore the previous > flags is obviously correct and only requires 2 runtime logic > operations because the compiler calculates the ~ operation on the > constant. So why do it differently here? i.e.: > > current->flags = (current->flags & ~KSWAPD_PF_FLAGS) | flags; > I will change it as you suggested if Matthew doesn't have a different opinion, Matthew ? > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -3870,19 +3870,7 @@ static int kswapd(void *p) > > if (!cpumask_empty(cpumask)) > > set_cpus_allowed_ptr(tsk, cpumask); > > > > - /* > > - * Tell the memory management that we're a "memory allocator", > > - * and that if we need more memory we should get access to it > > - * regardless (see "__alloc_pages()"). "kswapd" should > > - * never get caught in the normal page freeing logic. > > - * > > - * (Kswapd normally doesn't need memory anyway, but sometimes > > - * you need a small amount of memory in order to be able to > > - * page out something else, and this flag essentially protects > > - * us from recursively trying to free more memory as we're > > - * trying to free the first piece of memory in the first place). > > - */ > > - tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; > > + become_kswapd(); > > set_freezable(); > > > > WRITE_ONCE(pgdat->kswapd_order, 0); > > @@ -3932,8 +3920,6 @@ static int kswapd(void *p) > > goto kswapd_try_sleep; > > } > > > > - tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD); > > - > > Missing a restore_kswapd()? > > Cheers, > > Dave. > -- > Dave Chinner > david@fromorbit.com
diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c index 51dbff9b0908..0f35b7a38e76 100644 --- a/fs/xfs/libxfs/xfs_btree.c +++ b/fs/xfs/libxfs/xfs_btree.c @@ -2813,8 +2813,9 @@ xfs_btree_split_worker( { struct xfs_btree_split_args *args = container_of(work, struct xfs_btree_split_args, work); + bool is_kswapd = args->kswapd; unsigned long pflags; - unsigned long new_pflags = PF_MEMALLOC_NOFS; + int memalloc_nofs; /* * we are in a transaction context here, but may also be doing work @@ -2822,16 +2823,17 @@ xfs_btree_split_worker( * temporarily to ensure that we don't block waiting for memory reclaim * in any way. */ - if (args->kswapd) - new_pflags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; - - current_set_flags_nested(&pflags, new_pflags); + if (is_kswapd) + pflags = become_kswapd(); + memalloc_nofs = memalloc_nofs_save(); args->result = __xfs_btree_split(args->cur, args->level, args->ptrp, args->key, args->curp, args->stat); complete(args->done); - current_restore_flags_nested(&pflags, new_pflags); + memalloc_nofs_restore(memalloc_nofs); + if (is_kswapd) + restore_kswapd(pflags); } /* diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h index d5ece7a9a403..2faf03e79a1e 100644 --- a/include/linux/sched/mm.h +++ b/include/linux/sched/mm.h @@ -278,6 +278,29 @@ static inline void memalloc_nocma_restore(unsigned int flags) } #endif +/* + * Tell the memory management code that this thread is working on behalf + * of background memory reclaim (like kswapd). That means that it will + * get access to memory reserves should it need to allocate memory in + * order to make forward progress. With this great power comes great + * responsibility to not exhaust those reserves. + */ +#define KSWAPD_PF_FLAGS (PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD) + +static inline unsigned long become_kswapd(void) +{ + unsigned long flags = current->flags & KSWAPD_PF_FLAGS; + + current->flags |= KSWAPD_PF_FLAGS; + + return flags; +} + +static inline void restore_kswapd(unsigned long flags) +{ + current->flags &= ~(flags ^ KSWAPD_PF_FLAGS); +} + #ifdef CONFIG_MEMCG DECLARE_PER_CPU(struct mem_cgroup *, int_active_memcg); /** diff --git a/mm/vmscan.c b/mm/vmscan.c index 7b4e31eac2cf..15af99d1f3f7 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3870,19 +3870,7 @@ static int kswapd(void *p) if (!cpumask_empty(cpumask)) set_cpus_allowed_ptr(tsk, cpumask); - /* - * Tell the memory management that we're a "memory allocator", - * and that if we need more memory we should get access to it - * regardless (see "__alloc_pages()"). "kswapd" should - * never get caught in the normal page freeing logic. - * - * (Kswapd normally doesn't need memory anyway, but sometimes - * you need a small amount of memory in order to be able to - * page out something else, and this flag essentially protects - * us from recursively trying to free more memory as we're - * trying to free the first piece of memory in the first place). - */ - tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; + become_kswapd(); set_freezable(); WRITE_ONCE(pgdat->kswapd_order, 0); @@ -3932,8 +3920,6 @@ static int kswapd(void *p) goto kswapd_try_sleep; } - tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD); - return 0; }