Messages in this thread | | | Date | Mon, 4 Nov 2013 10:08:18 +0000 | From | Mel Gorman <> | Subject | Re: [PATCH] mm: Do not walk all of system memory during show_mem |
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On Wed, Oct 16, 2013 at 06:11:56PM -0700, David Rientjes wrote: > On Wed, 16 Oct 2013, Mel Gorman wrote: > > > It has been reported on very large machines that show_mem is taking almost > > 5 minutes to display information. This is a serious problem if there is > > an OOM storm. The bulk of the cost is in show_mem doing a very expensive > > PFN walk to give us the following information > > > > Total RAM: Also available as totalram_pages > > Highmem pages: Also available as totalhigh_pages > > Reserved pages: Can be inferred from the zone structure > > Shared pages: PFN walk required > > Unshared pages: PFN walk required > > Quick pages: Per-cpu walk required > > > > Only the shared/unshared pages requires a full PFN walk but that information > > is useless. It is also inaccurate as page pins of unshared pages would > > be accounted for as shared. Even if the information was accurate, I'm > > struggling to think how the shared/unshared information could be useful > > for debugging OOM conditions. Maybe it was useful before rmap existed when > > reclaiming shared pages was costly but it is less relevant today. > > > > The PFN walk could be optimised a bit but why bother as the information is > > useless. This patch deletes the PFN walker and infers the total RAM, highmem > > and reserved pages count from struct zone. It omits the shared/unshared page > > usage on the grounds that it is useless. It also corrects the reporting > > of HighMem as HighMem/MovableOnly as ZONE_MOVABLE has similar problems to > > HighMem with respect to lowmem/highmem exhaustion. > > > > We haven't been hit by this for the oom killer, but we did get hit with > this for page allocation failure warnings as a result of having irqs > disabled and passing GFP_ATOMIC to the page allocator without GFP_NOWARN. > That was the intention of passing SHOW_MEM_FILTER_PAGE_COUNT into > show_mem() in 4b59e6c47309 ("mm, show_mem: suppress page counts in > non-blockable contexts"). > > With this, I assume we can just remove SHOW_MEM_FILTER_PAGE_COUNT > entirely?
We could once all the per-arch show_mem functions were updated similar to lib/show_mem.c. I've added a todo item to do just that. Thanks.
-- Mel Gorman SUSE Labs
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