Date: Mon, 25 Dec 2017 11:51:17 -0800 From: Mark Johnston <markj@FreeBSD.org> To: Peter Holm <peter@holm.cc> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r327168 - head/sys/vm Message-ID: <20171225195117.GA68801@wkstn-mjohnston.west.isilon.com> In-Reply-To: <20171225174946.GA9941@x2.osted.lan> References: <201712241945.vBOJjGV5051696@repo.freebsd.org> <20171225174946.GA9941@x2.osted.lan>
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On Mon, Dec 25, 2017 at 06:49:46PM +0100, Peter Holm wrote: > On Sun, Dec 24, 2017 at 07:45:16PM +0000, Mark Johnston wrote: > > Author: markj > > Date: Sun Dec 24 19:45:16 2017 > > New Revision: 327168 > > URL: https://svnweb.freebsd.org/changeset/base/327168 > > > > Log: > > Fix two problems with the page daemon control loop. > > > > Both issues caused the page daemon to erroneously go to sleep when > > applications are consuming free pages at a high rate, leaving the > > application threads blocked in VM_WAIT. > > > > 1) After completing an inactive queue scan, concurrent allocations may > > have prevented the page daemon from meeting the v_free_min threshold. > > In this case, the page daemon was going to sleep even when the > > inactive queue contained plenty of clean pages. > > 2) pagedaemon_wakeup() may be called without the free queues lock held. > > This can lead to a lost wakeup if a call occurs after the page daemon > > clears vm_pageout_wanted but before going to sleep. > > > > Fix 1) by ensuring that we start a new inactive queue scan immediately > > if v_free_count < v_free_min after a prior scan. > > > > Fix 2) by adding a new subroutine, pagedaemon_wait(), called from > > vm_wait() and vm_waitpfault(). It wakes up the page daemon if either > > vm_pages_needed or vm_pageout_wanted is false, and atomically sleeps > > on v_free_count. > > > > Reported by: jeff > > Reviewed by: alc > > MFC after: 2 weeks > > Differential Revision: https://reviews.freebsd.org/D13424 > > > > Modified: > > head/sys/vm/vm_page.c > > head/sys/vm/vm_pageout.c > > head/sys/vm/vm_pageout.h > > > > I now see threads blocked in VM_WAIT? > > https://people.freebsd.org/~pho/stress/log/mark013.txt Hmm, I don't see anything obviously wrong here. v_free_count is 38, well below the minimum threshold at which threads will block in VM_WAIT. The page daemon was running and vm_pages_needed is 1, which is expected. This just looks like a case of the page daemon failing to keep up with memory pressure. Do you not see threads entering VM_WAIT with this revision reverted?
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