From mboxrd@z Thu Jan 1 00:00:00 1970 From: Cong Wang Subject: Re: [RFC Patch] fs: implement per-file drop caches Date: Fri, 01 Jun 2012 19:32:17 +0800 Message-ID: <1338550337.17012.27.camel@cr0> References: <1338385120-14519-1-git-send-email-amwang@redhat.com> <4FC6393B.7090105@draigBrady.com> <1338445233.19369.21.camel@cr0> <4FC70FFE.50809@gmail.com> <1338466281.19369.44.camel@cr0> <4FC7C1CD.7020701@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Cc: =?ISO-8859-1?Q?P=E1draig?= Brady , linux-kernel@vger.kernel.org, Andrew Morton , Cong Wang , Alexander Viro , Matthew Wilcox , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org To: KOSAKI Motohiro Return-path: In-Reply-To: <4FC7C1CD.7020701@gmail.com> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Thu, 2012-05-31 at 15:09 -0400, KOSAKI Motohiro wrote: > (5/31/12 8:11 AM), Cong Wang wrote: > > On Thu, 2012-05-31 at 02:30 -0400, KOSAKI Motohiro wrote: > >> (5/31/12 2:20 AM), Cong Wang wrote: > >>> On Wed, 2012-05-30 at 16:14 +0100, P=C3=A1draig 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 i= t is > >>> using a totally different way to drop page caches, that is to inval= idate > >>> 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 patc= h, 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. More= omover > >> madvise(2) is cleaner than fcntl(2). > >> > > > > I think madvise(DONTNEED) attacks the problem in a different approach= , > > it munmaps the file mapping and by the way drops the page caches, my > > approach is to drop the page caches directly similar to what sysctl > > drop_caches. > > > > What about private file mapping? Could madvise(DONTNEED) drop the pag= e > > caches too even when the other process is doing the same private file > > mapping? At least my patch could do this. >=20 > Right. But a process can makes another mappings if a process have enoug= h > permission. and if it doesn't, a process shouldn't be able to drop a sh= ared > cache. >=20 Ok, then this patch is not a dup of madvise(DONTNEED). >=20 > > I am not sure if fcntl() is a good interface either, this is why the > > patch is marked as RFC. :-D >=20 > But, if you can find certain usecase, I'm not against anymore. >=20 Yeah, at least John Stoffel expressed his interests on this, as a sysadmin. So I believe there are some people need it. Now the problem is that I don't find a proper existing utility to patch, maybe P=C3=A1draig has any hints on this? Could this feature be merged in= to some core utility? Or I have to write a new utility for this? Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter= .ca/ Don't email: email@kvack.org