Messages in this thread | | | Subject | Re: [RFC Patch] fs: implement per-file drop caches | From | Cong Wang <> | Date | Thu, 31 May 2012 14:28:16 +0800 |
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On Wed, 2012-05-30 at 11:12 -0400, John Stoffel wrote: > Cong> This is a draft patch of implementing per-file drop caches. > > Interesting. So can I do this from outside a process? I'm a > SysAdmin, so my POV is from noticing, finding and fixing performance > problems when the system is under pressure.
Yes, sure, we need to write a utility (or patch an existing one) to do this for you admins.
> > Cong> It introduces a new fcntl command F_DROP_CACHES to drop > Cong> file caches of a specific file. The reason is that currently > Cong> we only have a system-wide drop caches interface, it could > Cong> cause system-wide performance down if we drop all page caches > Cong> when we actually want to drop the caches of some huge file. > > How can I tell how much cache is used by a file? And what is the > performance impact of this when run on a busy system? And what does > this patch buy us since I figure the VM should already be dropping > caches once the system comes under mem pressure... >
AFAIK, we don't export such information to user-space, we only have system-wide statistics.
Keiichi (in Cc) once wrote a patch to implement page cache tracepoint: http://marc.info/?l=linux-mm&m=131102496904326&w=3
but the patches are still not in upstream.
Thanks!
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