Date: Thu, 30 Nov 2017 16:01:31 -0500 From: Mark Johnston <markj@FreeBSD.org> To: Larry McVoy <lm@mcvoy.com> Cc: Warner Losh <imp@bsdimp.com>, Scott Long <scottl@netflix.com>, Kevin Bowling <kbowling@llnw.com>, Drew Gallatin <gallatin@netflix.com>, "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: small patch for pageout. Comments? Message-ID: <20171130210131.GC21606@raichu> In-Reply-To: <20171130205041.GA3924@mcvoy.com> References: <20171130173424.GA811@mcvoy.com> <CANCZdfqL9ZsKTfFi%2BvsCTh3yaNjtwaYYY3fvivdbNybBnujawg@mail.gmail.com> <20171130184923.GA30262@mcvoy.com> <20171130204750.GB21606@raichu> <20171130205041.GA3924@mcvoy.com>
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On Thu, Nov 30, 2017 at 12:50:41PM -0800, Larry McVoy wrote: > On Thu, Nov 30, 2017 at 03:47:50PM -0500, Mark Johnston wrote: > > > I dunno if there is a "right amount". I could make it a little smarter by > > > keeping track of how many pages we freed and sleep if we freed none in a > > > scan (which seems really unlikely). > > > > This situation can happen if the inactive queue is full of dirty pages. > > A problem with your patch is that we might not give enough time to the > > laundry thread (the thread responsible for writing the contents of dirty > > pages to disk and returning them to inactive queue for the page daemon > > to free) to write out dirty pages. In this case we might trigger the OOM > > killer prematurely, and in fact this scenario is what motivated r300865. > > So I would argue that we do in fact need to sleep if the page daemon is > > failing to make progress, in order to give time for I/O to complete. > > OK, that sounds reasonable. So what defines progress? v_dfree not > increasing? Is one page freed progress? One page freed is progress. We currently invoke the OOM killer only when the page daemon is making no progress. This turns out to be too conservative, which is what kib's patch attempts to address. wrt your patch, I'm saying that I think we should still sleep after a scan that failed to free any pages.
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