From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: dirty balancing deadlock Message-Id: From: Miklos Szeredi Date: Sun, 18 Feb 2007 19:28:18 +0100 Sender: owner-linux-mm@kvack.org Return-Path: To: linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: akpm@linux-foundation.org List-ID: I was testing the new fuse shared writable mmap support, and finding that bash-shared-mapping deadlocks (which isn't so strange ;). What is more strange is that this is not an OOM situation at all, with plenty of free and cached pages. A little more investigation shows that a similar deadlock happens reliably with bash-shared-mapping on a loopback mount, even if only half the total memory is used. The cause is slightly different in the two cases: - loopback mount: allocation by the underlying filesystem is stalled on throttle_vm_writeout() - fuse-loop: page dirtying on the underlying filesystem is stalled on balance_dirty_pages() In both cases the underlying fs is totally innocent, with no dirty/writback pages, yet it's waiting for the global dirty+writeback to go below the threshold, which obviously won't, until the allocation/dirtying succeeds. I'm not quite sure what the solution is, and asking for thoughts. Ideas: - per filesystem dirty counters. If filesystem is clean (or dirty is below some minimum), then balance_dirty_pages() should no wait any more - throttle_vm_writeout() was meant to throttle swapping, no? So in that case there should be a separate swap-writback counter Thanks, Miklos -- 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