| Message ID | 20200522035029.3022405-15-david@fromorbit.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | xfs: rework inode flushing to make inode reclaim fully asynchronous | expand |
On Fri, May 22, 2020 at 01:50:19PM +1000, Dave Chinner wrote: > From: Dave Chinner <dchinner@redhat.com> > > We no longer need to issue IO from shrinker based inode reclaim to > prevent spurious OOM killer invocation. This leaves only the global > filesystem management operations such as unmount needing to > writeback dirty inodes and reclaim them. > > Instead of using the reclaim pass to write dirty inodes before > reclaiming them, use the AIL to push all the dirty inodes before we > try to reclaim them. This allows us to remove all the conditional > SYNC_WAIT locking and the writeback code from xfs_reclaim_inode() > and greatly simplify the checks we need to do to reclaim an inode. > > Signed-off-by: Dave Chinner <dchinner@redhat.com> > --- > fs/xfs/xfs_icache.c | 116 +++++++++++--------------------------------- > 1 file changed, 29 insertions(+), 87 deletions(-) > > diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c > index 0f0f8fcd61b03..ee9bc82a0dfbe 100644 > --- a/fs/xfs/xfs_icache.c > +++ b/fs/xfs/xfs_icache.c > @@ -1130,24 +1130,17 @@ xfs_reclaim_inode_grab( > * dirty, async => requeue > * dirty, sync => flush, wait and reclaim > */ The function comment probably ought to describe what the two return values mean. true when the inode was freed and false if we need to try again, right? > -STATIC int > +static bool > xfs_reclaim_inode( > struct xfs_inode *ip, > struct xfs_perag *pag, > int sync_mode) > { > - struct xfs_buf *bp = NULL; > xfs_ino_t ino = ip->i_ino; /* for radix_tree_delete */ > - int error; > > -restart: > - error = 0; > xfs_ilock(ip, XFS_ILOCK_EXCL); > - if (!xfs_iflock_nowait(ip)) { > - if (!(sync_mode & SYNC_WAIT)) > - goto out; > - xfs_iflock(ip); > - } > + if (!xfs_iflock_nowait(ip)) > + goto out; > > if (XFS_FORCED_SHUTDOWN(ip->i_mount)) { > xfs_iunpin_wait(ip); > @@ -1155,51 +1148,19 @@ xfs_reclaim_inode( > xfs_iflush_abort(ip); > goto reclaim; > } > - if (xfs_ipincount(ip)) { > - if (!(sync_mode & SYNC_WAIT)) > - goto out_ifunlock; > - xfs_iunpin_wait(ip); > - } > + if (xfs_ipincount(ip)) > + goto out_ifunlock; > if (xfs_iflags_test(ip, XFS_ISTALE) || xfs_inode_clean(ip)) { > xfs_ifunlock(ip); > goto reclaim; > } > > - /* > - * Never flush out dirty data during non-blocking reclaim, as it would > - * just contend with AIL pushing trying to do the same job. > - */ > - if (!(sync_mode & SYNC_WAIT)) > - goto out_ifunlock; > - > - /* > - * Now we have an inode that needs flushing. > - * > - * Note that xfs_iflush will never block on the inode buffer lock, as > - * xfs_ifree_cluster() can lock the inode buffer before it locks the > - * ip->i_lock, and we are doing the exact opposite here. As a result, > - * doing a blocking xfs_imap_to_bp() to get the cluster buffer would > - * result in an ABBA deadlock with xfs_ifree_cluster(). > - * > - * As xfs_ifree_cluser() must gather all inodes that are active in the > - * cache to mark them stale, if we hit this case we don't actually want > - * to do IO here - we want the inode marked stale so we can simply > - * reclaim it. Hence if we get an EAGAIN error here, just unlock the > - * inode, back off and try again. Hopefully the next pass through will > - * see the stale flag set on the inode. > - */ > - error = xfs_iflush(ip, &bp); > - if (error == -EAGAIN) { > - xfs_iunlock(ip, XFS_ILOCK_EXCL); > - /* backoff longer than in xfs_ifree_cluster */ > - delay(2); > - goto restart; > - } > - > - if (!error) { > - error = xfs_bwrite(bp); > - xfs_buf_relse(bp); > - } > +out_ifunlock: > + xfs_ifunlock(ip); > +out: > + xfs_iunlock(ip, XFS_ILOCK_EXCL); > + xfs_iflags_clear(ip, XFS_IRECLAIM); > + return false; > > reclaim: > ASSERT(!xfs_isiflocked(ip)); > @@ -1249,21 +1210,7 @@ xfs_reclaim_inode( > xfs_iunlock(ip, XFS_ILOCK_EXCL); > > __xfs_inode_free(ip); > - return error; > - > -out_ifunlock: > - xfs_ifunlock(ip); > -out: > - xfs_iflags_clear(ip, XFS_IRECLAIM); > - xfs_iunlock(ip, XFS_ILOCK_EXCL); > - /* > - * We could return -EAGAIN here to make reclaim rescan the inode tree in > - * a short while. However, this just burns CPU time scanning the tree > - * waiting for IO to complete and the reclaim work never goes back to > - * the idle state. Instead, return 0 to let the next scheduled > - * background reclaim attempt to reclaim the inode again. > - */ > - return 0; > + return true; > } > > /* > @@ -1272,20 +1219,17 @@ xfs_reclaim_inode( > * then a shut down during filesystem unmount reclaim walk leak all the > * unreclaimed inodes. > */ > -STATIC int > +static int The function comment /really/ needs to note that the return value here is number of inodes that were skipped, and not just some negative error code. > xfs_reclaim_inodes_ag( > struct xfs_mount *mp, > int flags, > int *nr_to_scan) > { > struct xfs_perag *pag; > - int error = 0; > - int last_error = 0; > xfs_agnumber_t ag; > int trylock = flags & SYNC_TRYLOCK; > int skipped; > > -restart: > ag = 0; > skipped = 0; > while ((pag = xfs_perag_get_tag(mp, ag, XFS_ICI_RECLAIM_TAG))) { > @@ -1359,9 +1303,8 @@ xfs_reclaim_inodes_ag( > for (i = 0; i < nr_found; i++) { > if (!batch[i]) > continue; > - error = xfs_reclaim_inode(batch[i], pag, flags); > - if (error && last_error != -EFSCORRUPTED) > - last_error = error; > + if (!xfs_reclaim_inode(batch[i], pag, flags)) > + skipped++; > } > > *nr_to_scan -= XFS_LOOKUP_BATCH; > @@ -1377,19 +1320,7 @@ xfs_reclaim_inodes_ag( > mutex_unlock(&pag->pag_ici_reclaim_lock); > xfs_perag_put(pag); > } > - > - /* > - * if we skipped any AG, and we still have scan count remaining, do > - * another pass this time using blocking reclaim semantics (i.e > - * waiting on the reclaim locks and ignoring the reclaim cursors). This > - * ensure that when we get more reclaimers than AGs we block rather > - * than spin trying to execute reclaim. > - */ > - if (skipped && (flags & SYNC_WAIT) && *nr_to_scan > 0) { > - trylock = 0; > - goto restart; > - } > - return last_error; > + return skipped; > } > > int > @@ -1398,8 +1329,18 @@ xfs_reclaim_inodes( > int mode) > { > int nr_to_scan = INT_MAX; > + int skipped; > > - return xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan); > + skipped = xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan); > + if (!(mode & SYNC_WAIT)) > + return 0; > + > + do { > + xfs_ail_push_all_sync(mp->m_ail); > + skipped = xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan); > + } while (skipped > 0); > + > + return 0; Might as well kill the return value here since none of the callers care. > } > > /* > @@ -1420,7 +1361,8 @@ xfs_reclaim_inodes_nr( > xfs_reclaim_work_queue(mp); > xfs_ail_push_all(mp->m_ail); > > - return xfs_reclaim_inodes_ag(mp, SYNC_TRYLOCK, &nr_to_scan); So the old code was returning negative error codes here? Given that the only caller is free_cached_objects which adds it to the 'freed' count... wow. > + xfs_reclaim_inodes_ag(mp, SYNC_TRYLOCK, &nr_to_scan); > + return 0; Why do we return zero freed items here? The VFS asked us to clear shrink_control->nr_to_scan (passed in here as nr_to_scan) and we're supposed to report what we did, right? Or is there some odd subtlety here where we hate the shrinker and that's why we return zero? --D > } > > /* > -- > 2.26.2.761.g0e0b3e54be >
> +out_ifunlock: > + xfs_ifunlock(ip); > +out: > + xfs_iunlock(ip, XFS_ILOCK_EXCL); > + xfs_iflags_clear(ip, XFS_IRECLAIM); > + return false; > > reclaim: I find the reordering of the error handling to sit before the actual reclaim action here really weird to read. What about something like this folded in instead? diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c index 9bb022a3570a3..6f873eca8c916 100644 --- a/fs/xfs/xfs_icache.c +++ b/fs/xfs/xfs_icache.c @@ -1091,18 +1091,10 @@ xfs_reclaim_inode( } if (xfs_ipincount(ip)) goto out_ifunlock; - if (xfs_iflags_test(ip, XFS_ISTALE) || xfs_inode_clean(ip)) { - xfs_ifunlock(ip); - goto reclaim; - } + if (!xfs_inode_clean(ip) && !xfs_iflags_test(ip, XFS_ISTALE)) + goto out_ifunlock; -out_ifunlock: xfs_ifunlock(ip); -out_iunlock: - xfs_iunlock(ip, XFS_ILOCK_EXCL); -out: - xfs_iflags_clear(ip, XFS_IRECLAIM); - return false; reclaim: ASSERT(!xfs_isiflocked(ip)); @@ -1153,6 +1145,14 @@ xfs_reclaim_inode( __xfs_inode_free(ip); return true; + +out_ifunlock: + xfs_ifunlock(ip); +out_iunlock: + xfs_iunlock(ip, XFS_ILOCK_EXCL); +out: + xfs_iflags_clear(ip, XFS_IRECLAIM); + return false; } /*
On Sat, May 23, 2020 at 02:40:55AM -0700, Christoph Hellwig wrote: > > +out_ifunlock: > > + xfs_ifunlock(ip); > > +out: > > + xfs_iunlock(ip, XFS_ILOCK_EXCL); > > + xfs_iflags_clear(ip, XFS_IRECLAIM); > > + return false; > > > > reclaim: > > I find the reordering of the error handling to sit before the actual > reclaim action here really weird to read. What about something like > this folded in instead? Yeah, once the writeback restart goes away, it does look somewhat weird. I've been considering pulling the actual inode reclaim code into it's own function, just to separate it from the "try-lock and check if we can reclaim this inode" operations. I'll have a look and see what falls out... Cheers, Dave.
On Fri, May 22, 2020 at 04:06:42PM -0700, Darrick J. Wong wrote: > On Fri, May 22, 2020 at 01:50:19PM +1000, Dave Chinner wrote: > > From: Dave Chinner <dchinner@redhat.com> > > > > We no longer need to issue IO from shrinker based inode reclaim to > > prevent spurious OOM killer invocation. This leaves only the global > > filesystem management operations such as unmount needing to > > writeback dirty inodes and reclaim them. > > > > Instead of using the reclaim pass to write dirty inodes before > > reclaiming them, use the AIL to push all the dirty inodes before we > > try to reclaim them. This allows us to remove all the conditional > > SYNC_WAIT locking and the writeback code from xfs_reclaim_inode() > > and greatly simplify the checks we need to do to reclaim an inode. > > > > Signed-off-by: Dave Chinner <dchinner@redhat.com> > > --- > > fs/xfs/xfs_icache.c | 116 +++++++++++--------------------------------- > > 1 file changed, 29 insertions(+), 87 deletions(-) > > > > diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c > > index 0f0f8fcd61b03..ee9bc82a0dfbe 100644 > > --- a/fs/xfs/xfs_icache.c > > +++ b/fs/xfs/xfs_icache.c > > @@ -1130,24 +1130,17 @@ xfs_reclaim_inode_grab( > > * dirty, async => requeue > > * dirty, sync => flush, wait and reclaim > > */ > > The function comment probably ought to describe what the two return > values mean. true when the inode was freed and false if we need to try > again, right? The comments are all updated in a later patch. It seemed better to do that than to have to rewrite the repeatedly as behaviour changes in each patch. > > @@ -1272,20 +1219,17 @@ xfs_reclaim_inode( > > * then a shut down during filesystem unmount reclaim walk leak all the > > * unreclaimed inodes. > > */ > > -STATIC int > > +static int > > The function comment /really/ needs to note that the return value > here is number of inodes that were skipped, and not just some negative > error code. OK, done. > > @@ -1398,8 +1329,18 @@ xfs_reclaim_inodes( > > int mode) > > { > > int nr_to_scan = INT_MAX; > > + int skipped; > > > > - return xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan); > > + skipped = xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan); > > + if (!(mode & SYNC_WAIT)) > > + return 0; > > + > > + do { > > + xfs_ail_push_all_sync(mp->m_ail); > > + skipped = xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan); > > + } while (skipped > 0); > > + > > + return 0; > > Might as well kill the return value here since none of the callers care. I think I did that in the SYNC_WAIT futzing patches that were causing me problems and I dropped. It was in a separate patch, anyway. > > } > > > > /* > > @@ -1420,7 +1361,8 @@ xfs_reclaim_inodes_nr( > > xfs_reclaim_work_queue(mp); > > xfs_ail_push_all(mp->m_ail); > > > > - return xfs_reclaim_inodes_ag(mp, SYNC_TRYLOCK, &nr_to_scan); > > So the old code was returning negative error codes here? Given that the > only caller is free_cached_objects which adds it to the 'freed' count... > wow. Actually, no. the error from xfs_reclaim_inodes_ag() can only come from xfs_reclaim_inode(), which always returned 0. > > + xfs_reclaim_inodes_ag(mp, SYNC_TRYLOCK, &nr_to_scan); > > + return 0; > > Why do we return zero freed items here? The VFS asked us to clear > shrink_control->nr_to_scan (passed in here as nr_to_scan) and we're > supposed to report what we did, right? It's the same behaviour as we currently have. ISTR that I did the accounting this way originally so we didn't double count inodes being freed. The inode has already been accounted as freed by the VFS inode shrinker when it runs ->destroy_inode, so double counting every inode that is freed (once for the VFS cache removal, once for the XFS cache removal) seemed like a bad thing to be doing... > Or is there some odd subtlety here where we hate the shrinker and that's > why we return zero? Oh, that too :P Cheers, Dave.
diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c index 0f0f8fcd61b03..ee9bc82a0dfbe 100644 --- a/fs/xfs/xfs_icache.c +++ b/fs/xfs/xfs_icache.c @@ -1130,24 +1130,17 @@ xfs_reclaim_inode_grab( * dirty, async => requeue * dirty, sync => flush, wait and reclaim */ -STATIC int +static bool xfs_reclaim_inode( struct xfs_inode *ip, struct xfs_perag *pag, int sync_mode) { - struct xfs_buf *bp = NULL; xfs_ino_t ino = ip->i_ino; /* for radix_tree_delete */ - int error; -restart: - error = 0; xfs_ilock(ip, XFS_ILOCK_EXCL); - if (!xfs_iflock_nowait(ip)) { - if (!(sync_mode & SYNC_WAIT)) - goto out; - xfs_iflock(ip); - } + if (!xfs_iflock_nowait(ip)) + goto out; if (XFS_FORCED_SHUTDOWN(ip->i_mount)) { xfs_iunpin_wait(ip); @@ -1155,51 +1148,19 @@ xfs_reclaim_inode( xfs_iflush_abort(ip); goto reclaim; } - if (xfs_ipincount(ip)) { - if (!(sync_mode & SYNC_WAIT)) - goto out_ifunlock; - xfs_iunpin_wait(ip); - } + if (xfs_ipincount(ip)) + goto out_ifunlock; if (xfs_iflags_test(ip, XFS_ISTALE) || xfs_inode_clean(ip)) { xfs_ifunlock(ip); goto reclaim; } - /* - * Never flush out dirty data during non-blocking reclaim, as it would - * just contend with AIL pushing trying to do the same job. - */ - if (!(sync_mode & SYNC_WAIT)) - goto out_ifunlock; - - /* - * Now we have an inode that needs flushing. - * - * Note that xfs_iflush will never block on the inode buffer lock, as - * xfs_ifree_cluster() can lock the inode buffer before it locks the - * ip->i_lock, and we are doing the exact opposite here. As a result, - * doing a blocking xfs_imap_to_bp() to get the cluster buffer would - * result in an ABBA deadlock with xfs_ifree_cluster(). - * - * As xfs_ifree_cluser() must gather all inodes that are active in the - * cache to mark them stale, if we hit this case we don't actually want - * to do IO here - we want the inode marked stale so we can simply - * reclaim it. Hence if we get an EAGAIN error here, just unlock the - * inode, back off and try again. Hopefully the next pass through will - * see the stale flag set on the inode. - */ - error = xfs_iflush(ip, &bp); - if (error == -EAGAIN) { - xfs_iunlock(ip, XFS_ILOCK_EXCL); - /* backoff longer than in xfs_ifree_cluster */ - delay(2); - goto restart; - } - - if (!error) { - error = xfs_bwrite(bp); - xfs_buf_relse(bp); - } +out_ifunlock: + xfs_ifunlock(ip); +out: + xfs_iunlock(ip, XFS_ILOCK_EXCL); + xfs_iflags_clear(ip, XFS_IRECLAIM); + return false; reclaim: ASSERT(!xfs_isiflocked(ip)); @@ -1249,21 +1210,7 @@ xfs_reclaim_inode( xfs_iunlock(ip, XFS_ILOCK_EXCL); __xfs_inode_free(ip); - return error; - -out_ifunlock: - xfs_ifunlock(ip); -out: - xfs_iflags_clear(ip, XFS_IRECLAIM); - xfs_iunlock(ip, XFS_ILOCK_EXCL); - /* - * We could return -EAGAIN here to make reclaim rescan the inode tree in - * a short while. However, this just burns CPU time scanning the tree - * waiting for IO to complete and the reclaim work never goes back to - * the idle state. Instead, return 0 to let the next scheduled - * background reclaim attempt to reclaim the inode again. - */ - return 0; + return true; } /* @@ -1272,20 +1219,17 @@ xfs_reclaim_inode( * then a shut down during filesystem unmount reclaim walk leak all the * unreclaimed inodes. */ -STATIC int +static int xfs_reclaim_inodes_ag( struct xfs_mount *mp, int flags, int *nr_to_scan) { struct xfs_perag *pag; - int error = 0; - int last_error = 0; xfs_agnumber_t ag; int trylock = flags & SYNC_TRYLOCK; int skipped; -restart: ag = 0; skipped = 0; while ((pag = xfs_perag_get_tag(mp, ag, XFS_ICI_RECLAIM_TAG))) { @@ -1359,9 +1303,8 @@ xfs_reclaim_inodes_ag( for (i = 0; i < nr_found; i++) { if (!batch[i]) continue; - error = xfs_reclaim_inode(batch[i], pag, flags); - if (error && last_error != -EFSCORRUPTED) - last_error = error; + if (!xfs_reclaim_inode(batch[i], pag, flags)) + skipped++; } *nr_to_scan -= XFS_LOOKUP_BATCH; @@ -1377,19 +1320,7 @@ xfs_reclaim_inodes_ag( mutex_unlock(&pag->pag_ici_reclaim_lock); xfs_perag_put(pag); } - - /* - * if we skipped any AG, and we still have scan count remaining, do - * another pass this time using blocking reclaim semantics (i.e - * waiting on the reclaim locks and ignoring the reclaim cursors). This - * ensure that when we get more reclaimers than AGs we block rather - * than spin trying to execute reclaim. - */ - if (skipped && (flags & SYNC_WAIT) && *nr_to_scan > 0) { - trylock = 0; - goto restart; - } - return last_error; + return skipped; } int @@ -1398,8 +1329,18 @@ xfs_reclaim_inodes( int mode) { int nr_to_scan = INT_MAX; + int skipped; - return xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan); + skipped = xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan); + if (!(mode & SYNC_WAIT)) + return 0; + + do { + xfs_ail_push_all_sync(mp->m_ail); + skipped = xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan); + } while (skipped > 0); + + return 0; } /* @@ -1420,7 +1361,8 @@ xfs_reclaim_inodes_nr( xfs_reclaim_work_queue(mp); xfs_ail_push_all(mp->m_ail); - return xfs_reclaim_inodes_ag(mp, SYNC_TRYLOCK, &nr_to_scan); + xfs_reclaim_inodes_ag(mp, SYNC_TRYLOCK, &nr_to_scan); + return 0; } /*