Adding Brian to cc On Wed, Oct 19, 2022 at 04:18:10PM -0700, Andrew Morton wrote: > On Wed, 19 Oct 2022 11:17:14 -0700 Yang Shi <shy828301@xxxxxxxxx> wrote: > > > > The intent of commit b653db77350c patch was to avoid the case where > > > PG_private is clear but folio->private is not-NULL. However, THP tail > > > pages uses page->private for "swp_entry_t if folio_test_swapcache()" as > > > stated in the documentation for struct folio. This patch only clobbers > > > page->private for tail pages if the head page was not in swapcache and > > > warns once if page->private had an unexpected value. > > > > It looks like the same issue fixed by > > https://lore.kernel.org/linux-mm/20220906190602.1626037-1-bfoster@xxxxxxxxxx/ > > It is. > Yep, based on Brian's changelog, it was the same workload that triggered it as it happens to stress the corner case that hits the bug. > As I asked earlier this week, what about reverting b653db77350c? Why > do we care about the value of ->private for non-PG_private pages? I don't think we do care but based on the changelog of b653db77350c, it's part of an effort to either remove the PG_private bit or is a preparation step for casting page to a meaningful type based on context but only Matthew can tell us his motivation. There at least is some value to identifying cases where a referenced page has valid information in page->private that is not reflected in the flags. -- Mel Gorman SUSE Labs
