On Wed, Aug 19, 2020 at 04:06:32PM -0700, Yang Shi wrote: > On Tue, Aug 18, 2020 at 11:47 AM Yu Zhao <yuzhao@xxxxxxxxxx> wrote: > > > > Presumably __ClearPageWaiters() was added to follow the previously > > removed __ClearPageActive() pattern. > > > > Only flags that are in PAGE_FLAGS_CHECK_AT_FREE needs to be properly > > cleared because otherwise we think there may be some kind of leak. > > PG_waiters is not one of those flags and leaving the clearing to > > PAGE_FLAGS_CHECK_AT_PREP is more appropriate. > > Actually TBH I'm not very keen to this change, it seems the clearing > is just moved around and the allocation side pays for that instead of > free side. I'll assume you are referring to the overhead from clearing PG_waiters. First of all, there is no overhead -- we should have a serious talk with the hardware team who makes word-size bitwise AND more than one instruction. And the clearing is done in free_pages_prepare(), which has nothing to do with allocations.
