Date: Tue, 06 May 2014 18:59:59 -0500 From: Alan Cox <alc@rice.edu> To: Ian Lepore <ian@FreeBSD.org>, Alan Cox <alc@FreeBSD.org> Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org Subject: Re: svn commit: r265418 - head/sys/vm Message-ID: <5369777F.6010203@rice.edu> In-Reply-To: <1399379941.22079.263.camel@revolution.hippie.lan> References: <201405060342.s463g5Fx047447@svn.freebsd.org> <1399379941.22079.263.camel@revolution.hippie.lan>
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On 05/06/2014 07:39, Ian Lepore wrote: > On Tue, 2014-05-06 at 03:42 +0000, Alan Cox wrote: >> Author: alc >> Date: Tue May 6 03:42:04 2014 >> New Revision: 265418 >> URL: http://svnweb.freebsd.org/changeset/base/265418 >> >> Log: >> Prior to r254304, a separate function, vm_pageout_page_stats(), was used to >> periodically update the reference status of the active pages. This function >> was called, instead of vm_pageout_scan(), when memory was not scarce. The >> objective was to provide up to date reference status for active pages in >> case memory did become scarce and active pages needed to be deactivated. >> >> The active page queue scan performed by vm_pageout_page_stats() was >> virtually identical to that performed by vm_pageout_scan(), and so r254304 >> eliminated vm_pageout_page_stats(). Instead, vm_pageout_scan() is >> called with the parameter "pass" set to zero. The intention was that when >> pass is zero, vm_pageout_scan() would only scan the active queue. However, >> the variable page_shortage can still be greater than zero when memory is not >> scarce and vm_pageout_scan() is called with pass equal to zero. >> Consequently, the inactive queue may be scanned and dirty pages laundered >> even though that was not intended by r254304. This revision fixes that. >> >> Reported by: avg >> MFC after: 1 week >> Sponsored by: EMC / Isilon Storage Division >> >> Modified: >> head/sys/vm/vm_pageout.c >> >> Modified: head/sys/vm/vm_pageout.c >> ============================================================================== >> --- head/sys/vm/vm_pageout.c Tue May 6 03:38:04 2014 (r265417) >> +++ head/sys/vm/vm_pageout.c Tue May 6 03:42:04 2014 (r265418) >> @@ -942,13 +942,15 @@ vm_pageout_scan(struct vm_domain *vmd, i >> */ >> addl_page_shortage = 0; >> >> - deficit = atomic_readandclear_int(&vm_pageout_deficit); >> - >> /* >> * Calculate the number of pages we want to either free or move >> * to the cache. >> */ >> - page_shortage = vm_paging_target() + deficit; >> + if (pass > 0) { >> + deficit = atomic_readandclear_int(&vm_pageout_deficit); >> + page_shortage = vm_paging_target() + deficit; >> + } else >> + page_shortage = deficit = 0; >> >> /* >> * maxlaunder limits the number of dirty pages we flush per scan. >> > Does this address the observation that several folks have made on > current@ that pages are being pushed to swap much more agressively than > in the past, even when the system doesn't seem short of memory? > I hope so. Please let me know if you see any difference. I also suspect that another side-effect of r254304 is that we are swapping out idle processes sooner, before memory has become scarce. Has anyone observed this behavior? Alanhome | help
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