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Date: Tue, 14 Sep 2010 19:14:44 +0900 (JST) From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> To: Mel Gorman <mel@....ul.ie> Cc: kosaki.motohiro@...fujitsu.com, KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>, linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, Linux Kernel List <linux-kernel@...r.kernel.org>, Rik van Riel <riel@...hat.com>, Johannes Weiner <hannes@...xchg.org>, Minchan Kim <minchan.kim@...il.com>, Wu Fengguang <fengguang.wu@...el.com>, Andrea Arcangeli <aarcange@...hat.com>, Dave Chinner <david@...morbit.com>, Chris Mason <chris.mason@...cle.com>, Christoph Hellwig <hch@....de>, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [PATCH 05/10] vmscan: Synchrounous lumpy reclaim use lock_page() instead trylock_page() > > example, > > > > __do_fault() > > { > > (snip) > > if (unlikely(!(ret & VM_FAULT_LOCKED))) > > lock_page(vmf.page); > > else > > VM_BUG_ON(!PageLocked(vmf.page)); > > > > /* > > * Should we do an early C-O-W break? > > */ > > page = vmf.page; > > if (flags & FAULT_FLAG_WRITE) { > > if (!(vma->vm_flags & VM_SHARED)) { > > anon = 1; > > if (unlikely(anon_vma_prepare(vma))) { > > ret = VM_FAULT_OOM; > > goto out; > > } > > page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, > > vma, address); > > > > Correct, this is a problem. I already had dropped the patch but thanks for > pointing out a deadlock because I was missing this case. Nothing stops the > page being faulted being sent to shrink_page_list() when alloc_page_vma() > is called. The deadlock might be hard to hit, but it's there. Yup, unfortunatelly. > > Afaik, detailed rule is, > > > > o kswapd can call lock_page() because they never take page lock outside vmscan > > lock_page_nosync as you point out in your next mail. While it can call > it, kswapd shouldn't because normally it avoids stalls but it would not > deadlock as a result of calling it. Agreed. > > o if try_lock() is successed, we can call lock_page_nosync() against its page after unlock. > > because the task have gurantee of no lock taken. > > o otherwise, direct reclaimer can't call lock_page(). the task may have a lock already. > > > > I think the safer bet is simply to say "direct reclaimers should not > call lock_page() because the fault path could be holding a lock on that > page already". Yup, agreed. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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