[lkml]   [2010]   [Nov]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [PATCH 3/3] mlock: avoid dirtying pages and triggering writeback
    On Wed, 2010-11-17 at 23:57 +1100, Nick Piggin wrote:
    > On Wed, Nov 17, 2010 at 04:23:58AM -0800, Michel Lespinasse wrote:
    > > When faulting in pages for mlock(), we want to break COW for anonymous
    > > or file pages within VM_WRITABLE, non-VM_SHARED vmas. However, there is
    > > no need to write-fault into VM_SHARED vmas since shared file pages can
    > > be mlocked first and dirtied later, when/if they actually get written to.
    > > Skipping the write fault is desirable, as we don't want to unnecessarily
    > > cause these pages to be dirtied and queued for writeback.
    > It's not just to break COW, but to do block allocation and such
    > (filesystem's page_mkwrite op). That needs to at least be explained
    > in the changelog.

    Agreed, the 0/3 description actually does mention this.

    > Filesystem doesn't have a good way to fully pin required things
    > according to mlock, but page_mkwrite provides some reasonable things
    > (like block allocation / reservation).

    Right, but marking all pages dirty isn't really sane. I can imagine
    making the reservation but not marking things dirty solution, although
    it might be lots harder to implement, esp since some filesystems don't
    actually have a page_mkwrite() implementation.

     \ /
      Last update: 2010-11-17 16:31    [W:0.022 / U:10.944 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site