Date: Sun, 20 Apr 2003 12:10:29 -0700 From: David Schultz <das@freebsd.org> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: freebsd-current@freebsd.org Subject: Re: Broken memory management on system with no swap Message-ID: <20030420191029.GA4803@HAL9000.homeunix.com> In-Reply-To: <200304201828.h3KISlKq090099@apollo.backplane.com> References: <000501c30682$4e5e64b0$6601a8c0@VAIO650> <20030420002940.GB46590@HAL9000.homeunix.com> <20030420191744.G19683@gamplex.bde.org> <20030420101401.GA2821@HAL9000.homeunix.com> <200304201828.h3KISlKq090099@apollo.backplane.com>
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On Sun, Apr 20, 2003, Matthew Dillon wrote:
> Hmm. It sounds like this program is using mmap() to dirty pages and
> that the VM system is not flushing them out quickly enough to avoid
> running out of memory. This could happen if the program dirties
> a significant portion of memory all at once. The pageout daemon would
> wind up doing a priority requeue of the dirty pages (line 848 of
> vm_pageout.c) and 'miss' flushing any of them out to the filesystem
> in the first pass. The result would be that the system would believe
> it has run out of memory for a short period of time.
Thanks for your analysis. I thought there might be a GBDE-related
factor when Lucky mentioned that copying a file triggers the bug,
since cp(1) turns off mmap() mode for files > 8 MB to avoid this
sort of thing. But nevertheless, I can see how the situation you
describe can occur, where the system realizes too late that all of
the reclaimable pages are tied up in the active queue.
> I suggest changing this:
>
> if ((vm_swap_size < 64 && vm_page_count_min()) ||
> (swap_pager_full && vm_paging_target() > 0)) {
>
> To this:
>
> if (pass != 0 &&
> ((vm_swap_size < 64 && vm_page_count_min()) ||
> (swap_pager_full && vm_paging_target() > 0))) {
Sounds reasonable. I would be happy to look into this next month
if nobody else is interested. I would want to ensure that this
change cannot result in deadlock.
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