Messages in this thread |  | | | Subject | Re: [PATCH 3/3] mlock: avoid dirtying pages and triggering writeback | | From | Peter Zijlstra <> | | Date | Wed, 17 Nov 2010 16:28:54 +0100 |
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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.
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