From 1f6d64829db78a7e1d63e15c9f48f0a5d2b5a679 Mon Sep 17 00:00:00 2001 From: Dave Chinner Date: Fri, 6 Jun 2014 15:59:59 +1000 Subject: [PATCH] xfs: block allocation work needs to be kswapd aware Upon memory pressure, kswapd calls xfs_vm_writepage() from shrink_page_list(). This can result in delayed allocation occurring and that gets deferred to the the allocation workqueue. The allocation then runs outside kswapd context, which means if it needs memory (and it does to demand page metadata from disk) it can block in shrink_inactive_list() waiting for IO congestion. These blocking waits are normally avoiding in kswapd context, so under memory pressure writeback from kswapd can be arbitrarily delayed by memory reclaim. To avoid this, pass the kswapd context to the allocation being done by the workqueue, so that memory reclaim understands correctly that the work is being done for kswapd and therefore it is not blocked and does not delay memory reclaim. To avoid issues with int->char conversion of flag fields (as noticed in v1 of this patch) convert the flag fields in the struct xfs_bmalloca to bool types. pahole indicates these variables are still single byte variables, so no extra space is consumed by this change. cc: Reported-by: Tetsuo Handa Signed-off-by: Dave Chinner Reviewed-by: Christoph Hellwig Signed-off-by: Dave Chinner --- fs/xfs/xfs_bmap_util.c | 16 +++++++++++++--- fs/xfs/xfs_bmap_util.h | 13 +++++++------ 2 files changed, 20 insertions(+), 9 deletions(-) diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c index 296160b8e78c..47a9daa7b4e6 100644 --- a/fs/xfs/xfs_bmap_util.c +++ b/fs/xfs/xfs_bmap_util.c @@ -258,14 +258,23 @@ xfs_bmapi_allocate_worker( struct xfs_bmalloca *args = container_of(work, struct xfs_bmalloca, work); unsigned long pflags; + unsigned long new_pflags = PF_FSTRANS; - /* we are in a transaction context here */ - current_set_flags_nested(&pflags, PF_FSTRANS); + /* + * we are in a transaction context here, but may also be doing work + * in kswapd context, and hence we may need to inherit that state + * 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); args->result = __xfs_bmapi_allocate(args); complete(args->done); - current_restore_flags_nested(&pflags, PF_FSTRANS); + current_restore_flags_nested(&pflags, new_pflags); } /* @@ -284,6 +293,7 @@ xfs_bmapi_allocate( args->done = &done; + args->kswapd = current_is_kswapd(); INIT_WORK_ONSTACK(&args->work, xfs_bmapi_allocate_worker); queue_work(xfs_alloc_wq, &args->work); wait_for_completion(&done); diff --git a/fs/xfs/xfs_bmap_util.h b/fs/xfs/xfs_bmap_util.h index 935ed2b24edf..075f72232a64 100644 --- a/fs/xfs/xfs_bmap_util.h +++ b/fs/xfs/xfs_bmap_util.h @@ -50,12 +50,13 @@ struct xfs_bmalloca { xfs_extlen_t total; /* total blocks needed for xaction */ xfs_extlen_t minlen; /* minimum allocation size (blocks) */ xfs_extlen_t minleft; /* amount must be left after alloc */ - char eof; /* set if allocating past last extent */ - char wasdel; /* replacing a delayed allocation */ - char userdata;/* set if is user data */ - char aeof; /* allocated space at eof */ - char conv; /* overwriting unwritten extents */ - char stack_switch; + bool eof; /* set if allocating past last extent */ + bool wasdel; /* replacing a delayed allocation */ + bool userdata;/* set if is user data */ + bool aeof; /* allocated space at eof */ + bool conv; /* overwriting unwritten extents */ + bool stack_switch; + bool kswapd; /* allocation in kswapd context */ int flags; struct completion *done; struct work_struct work;