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? > > 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 :(
