Messages in this thread | | | Date | Thu, 31 May 2012 02:30:22 -0400 | From | KOSAKI Motohiro <> | Subject | Re: [RFC Patch] fs: implement per-file drop caches |
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(5/31/12 2:20 AM), Cong Wang wrote: > On Wed, 2012-05-30 at 16:14 +0100, Pádraig Brady wrote: >> On 05/30/2012 02:38 PM, Cong Wang wrote: >>> This is a draft patch of implementing per-file drop caches. >>> >>> It introduces a new fcntl command F_DROP_CACHES to drop >>> file caches of a specific file. The reason is that currently >>> we only have a system-wide drop caches interface, it could >>> cause system-wide performance down if we drop all page caches >>> when we actually want to drop the caches of some huge file. >> >> This is useful functionality. >> Though isn't it already provided with POSIX_FADV_DONTNEED? > > Thanks for teaching this! > > However, from the source code of madvise_dontneed() it looks like it is > using a totally different way to drop page caches, that is to invalidate > the page mapping, and trigger a re-mapping of the file pages after a > page fault. So, yeah, this could probably drop the page caches too (I am > not so sure, haven't checked the code in details), but with my patch, it > flushes the page caches directly, what's more, it can also prune > dcache/icache of the file.
madvise should work. I don't think we need duplicate interface. Moreomover madvise(2) is cleaner than fcntl(2).
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