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Open Source and information security mailing list archives
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Date: Tue, 18 Oct 2011 17:25:48 -0700 From: Andi Kleen <andi@...stfloor.org> To: Hugh Dickins <hughd@...gle.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Michel Lespinasse <walken@...gle.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org Subject: Re: [PATCH] mm: munlock use mapcount to avoid terrible overhead Hugh Dickins <hughd@...gle.com> writes: > A process spent 30 minutes exiting, just munlocking the pages of a large > anonymous area that had been alternately mprotected into page-sized vmas: > for every single page there's an anon_vma walk through all the other > little vmas to find the right one. We had the same problem recently after a mmap+touch workload: in this case it was hugepaged walking all these anon_vmas and the list was over 100k long. Had some data on this at plumbers: http://halobates.de/plumbers-fork-locks_v2.pdf > A general fix to that would be a lot more complicated (use prio_tree on > anon_vma?), but there's one very simple thing we can do to speed up the > common case: if a page to be munlocked is mapped only once, then it is > our vma that it is mapped into, and there's no need whatever to walk > through all the others. I think we need a generic fix, this problem does not only happen in munmap. -Andi -- ak@...ux.intel.com -- Speaking for myself only -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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