From mboxrd@z Thu Jan 1 00:00:00 1970 Message-Id: <20070504103202.718545249@chello.nl> References: <20070504102651.923946304@chello.nl> Date: Fri, 04 May 2007 12:27:22 +0200 From: Peter Zijlstra Subject: [PATCH 31/40] mm: balance_dirty_pages() vs throttle_vm_writeout() deadlock Content-Disposition: inline; filename=nfs_mm-throttle_vm_writeout.patch Sender: owner-linux-mm@kvack.org Return-Path: To: linux-kernel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org Cc: Peter Zijlstra , Trond Myklebust , Thomas Graf , David Miller , James Bottomley , Mike Christie , Andrew Morton , Daniel Phillips List-ID: 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(). Akpm's recent GFP checks don't much change this picture, any __GFP_IO|__GFP_FS alloc can still get stalled by this. It turns into a deadlock when swapping over NFS. 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 2007-03-06 17:44:23.000000000 +0100 +++ linux-2.6-git/mm/page-writeback.c 2007-03-15 15:09:16.000000000 +0100 @@ -320,8 +320,7 @@ void throttle_vm_writeout(gfp_t gfp_mask */ 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); } -- -- 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