From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: [RFC][PATCH] mm: balance_dirty_pages() vs throttle_vm_writeout() deadlock From: Peter Zijlstra In-Reply-To: <20070221160757.2183d23f.akpm@linux-foundation.org> References: <1171986565.23046.5.camel@twins> <20070221160757.2183d23f.akpm@linux-foundation.org> Content-Type: text/plain Date: Mon, 26 Feb 2007 14:43:58 +0100 Message-Id: <1172497438.6374.53.camel@twins> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Andrew Morton Cc: linux-mm@kvack.org, Trond Myklebust List-ID: On Wed, 2007-02-21 at 16:07 -0800, Andrew Morton wrote: > 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? > The deadlock seems to be elusive, I'll continue testing... > > 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; > _ Hmm, fun :-) It might, but I'm afraid that the NFS writeout path includes a GFP_ATOMIC allocation, in which case this would not suffice. I'll trace the paths again to make sure. (To be more specific, in patch 28/29 in the swap over NFS series the net/sunrpc/sched.c::rpc_malloc() bit) -- 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