On 10/18/18 6:47 PM, Andrew Morton wrote: > On Thu, 18 Oct 2018 20:46:21 -0400 Andrea Arcangeli <aarcange@xxxxxxxxxx> wrote: > >> On Thu, Oct 18, 2018 at 04:16:40PM -0700, Mike Kravetz wrote: >>> I was not sure about this, and expected someone could come up with >>> something better. It just seems there are filesystems like huegtlbfs, >>> where it makes no sense wasting cycles traversing the filesystem. So, >>> let's not even try. >>> >>> Hoping someone can come up with a better method than hard coding as >>> I have done above. >> >> It's not strictly required after marking the pages dirty though. The >> real fix is the other one? Could we just drop the hardcoding and let >> it run after the real fix is applied? Yeah. The other part of the patch is the real fix. This drop_caches part is not necessary. >> The performance of drop_caches doesn't seem critical, especially with >> gigapages. tmpfs doesn't seem to be optimized away from drop_caches >> and the gain would be bigger for tmpfs if THP is not enabled in the >> mount, so I'm not sure if we should worry about hugetlbfs first. > > I guess so. I can't immediately see a clean way of expressing this so > perhaps it would need a new BDI_CAP_NO_BACKING_STORE. Such a > thing hardly seems worthwhile for drop_caches. > > And drop_caches really shouldn't be there anyway. It's a standing > workaround for ongoing suckage in pagecache and metadata reclaim > behaviour :( I'm OK with dropping the other part. It just seemed like there was no real reason to try and drop_caches for hugetlbfs (and perhaps others). Andrew, would you like another version? Or can you just drop the fs/drop_caches.c part? -- Mike Kravetz
