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, 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). > >> > > > > 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 page > > caches too even when the other process is doing the same private file > > mapping? At least my patch could do this. > > Right. But a process can makes another mappings if a process have enough > permission. and if it doesn't, a process shouldn't be able to drop a shared > cache. > Ok, then this patch is not a dup of madvise(DONTNEED). > > > I am not sure if fcntl() is a good interface either, this is why the > > patch is marked as RFC. :-D > > But, if you can find certain usecase, I'm not against anymore. > 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 Pádraig has any hints on this? Could this feature be merged into some core utility? Or I have to write a new utility for this? Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
