On Wed, Aug 19, 2020 at 4:39 PM Yu Zhao <yuzhao@xxxxxxxxxx> wrote: > > 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. Oh, yes, you are right. Now I'm wondering why we have the waiter bit cleared at the first place.
