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Message-ID: <20081003145029.GE18542@agk.fab.redhat.com> Date: Fri, 3 Oct 2008 15:50:29 +0100 From: Alasdair G Kergon <agk@...hat.com> To: Mikulas Patocka <mpatocka@...hat.com> Cc: Nick Piggin <nickpiggin@...oo.com.au>, Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, agk@...hat.com, mbroz@...hat.com, chris@...chsys.com Subject: Re: [PATCH] Memory management livelock On Fri, Oct 03, 2008 at 09:50:17AM -0400, Mikulas Patocka wrote: > > > LVM does (that is where the bug was discovered). Basically, it scans all > > > the block devices with direct IO and if someone else does buffered IO on > > > any device simultaneously, it locks up. > > Scans all block devices with direct IO? Hmm, why, I wonder? Should > > really consider using buffered (posix_fadvise to readahead/dropbehind). > LVM must not allocate any memory when doing IO because it suspends the > block device and memory allocation could trigger writeback on the > suspended device and deadlock. > So it preallocates heap and stack, mlockall()s itself and does direct IO. True, but unrelated to the scanning, which LVM performs *prior* to entering such a state. We use direct IO while scanning because it's essential all nodes in a cluster see the same updated version of the data after any node updated it. Alasdair -- agk@...hat.com -- 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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