From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Wed, 21 Feb 2007 16:07:57 -0800 From: Andrew Morton Subject: Re: [RFC][PATCH] mm: balance_dirty_pages() vs throttle_vm_writeout() deadlock Message-Id: <20070221160757.2183d23f.akpm@linux-foundation.org> In-Reply-To: <1171986565.23046.5.camel@twins> References: <1171986565.23046.5.camel@twins> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Peter Zijlstra Cc: linux-mm@kvack.org, Trond Myklebust List-ID: On Tue, 20 Feb 2007 16:49:24 +0100 Peter Zijlstra wrote: > > If we have a lot of dirty memory and hit the throttle in balance_dirty_pages() > we (potentially) generate a lot of writeback and unstable pages, if however > during this writeback we need to reclaim a bit, we might hit > throttle_vm_writeout(), which might delay us until the combined total of > NR_UNSTABLE_NFS + NR_WRITEBACK falls below the dirty limit. > > However unstable pages don't go away automagickally, they need a push. While > balance_dirty_pages() does this push, throttle_vm_writeout() doesn't. So we can > sit here ad infintum. > > Hence I propose to remove the NR_UNSTABLE_NFS count from throttle_vm_writeout(). > > Signed-off-by: Peter Zijlstra > --- > mm/page-writeback.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > Index: linux-2.6-git/mm/page-writeback.c > =================================================================== > --- linux-2.6-git.orig/mm/page-writeback.c 2007-02-20 15:07:43.000000000 +0100 > +++ linux-2.6-git/mm/page-writeback.c 2007-02-20 16:42:45.000000000 +0100 > @@ -310,8 +310,7 @@ void throttle_vm_writeout(void) > */ > dirty_thresh += dirty_thresh / 10; /* wheeee... */ > > - if (global_page_state(NR_UNSTABLE_NFS) + > - global_page_state(NR_WRITEBACK) <= dirty_thresh) > + if (global_page_state(NR_WRITEBACK) <= dirty_thresh) > break; > congestion_wait(WRITE, HZ/10); > } I think we need the below. It is to address a deadlock which usb-storage triggered doing a GFP_NOIO allocation, but I suspect it'll fix NFS too? From: Andrew Morton throttle_vm_writeout() is designed to wait for the dirty levels to subside. But if the caller holds IO or FS locks, we might be holding up that writeout. So change it to take a single nap to give other devices a chance to clean some memory, then return. Cc: Nick Piggin Cc: OGAWA Hirofumi Cc: Kumar Gala Cc: Pete Zaitcev Signed-off-by: Andrew Morton --- include/linux/writeback.h | 2 +- mm/page-writeback.c | 13 +++++++++++-- mm/vmscan.c | 2 +- 3 files changed, 13 insertions(+), 4 deletions(-) diff -puN mm/vmscan.c~throttle_vm_writeout-dont-loop-on-gfp_nofs-and-gfp_noio-allocations mm/vmscan.c --- a/mm/vmscan.c~throttle_vm_writeout-dont-loop-on-gfp_nofs-and-gfp_noio-allocations +++ a/mm/vmscan.c @@ -952,7 +952,7 @@ static unsigned long shrink_zone(int pri } } - throttle_vm_writeout(); + throttle_vm_writeout(sc->gfp_mask); atomic_dec(&zone->reclaim_in_progress); return nr_reclaimed; diff -puN mm/page-writeback.c~throttle_vm_writeout-dont-loop-on-gfp_nofs-and-gfp_noio-allocations mm/page-writeback.c --- a/mm/page-writeback.c~throttle_vm_writeout-dont-loop-on-gfp_nofs-and-gfp_noio-allocations +++ a/mm/page-writeback.c @@ -296,11 +296,21 @@ void balance_dirty_pages_ratelimited_nr( } EXPORT_SYMBOL(balance_dirty_pages_ratelimited_nr); -void throttle_vm_writeout(void) +void throttle_vm_writeout(gfp_t gfp_mask) { long background_thresh; long dirty_thresh; + if ((gfp_mask & (__GFP_FS|__GFP_IO)) != ) { + /* + * The caller might hold locks which can prevent IO completion + * or progress in the filesystem. So we cannot just sit here + * waiting for IO to complete. + */ + congestion_wait(WRITE, HZ/10); + return; + } + for ( ; ; ) { get_dirty_limits(&background_thresh, &dirty_thresh, NULL); @@ -317,7 +327,6 @@ void throttle_vm_writeout(void) } } - /* * writeback at least _min_pages, and keep writing until the amount of dirty * memory is less than the background threshold, or until we're all clean. diff -puN include/linux/writeback.h~throttle_vm_writeout-dont-loop-on-gfp_nofs-and-gfp_noio-allocations include/linux/writeback.h --- a/include/linux/writeback.h~throttle_vm_writeout-dont-loop-on-gfp_nofs-and-gfp_noio-allocations +++ a/include/linux/writeback.h @@ -84,7 +84,7 @@ static inline void wait_on_inode(struct int wakeup_pdflush(long nr_pages); void laptop_io_completion(void); void laptop_sync_completion(void); -void throttle_vm_writeout(void); +void throttle_vm_writeout(gfp_t gfp_mask); /* These are exported to sysctl. */ extern int dirty_background_ratio; _ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org