On Wed, Dec 09, 2020 at 08:40:05AM +0000, Christoph Hellwig wrote: > > + /* > > + * In practice groups of pages tend to be accessed/reclaimed/refaulted > > + * together. To not go over bvec for those who didn't set BIO_WORKINGSET > > + * approximate it by looking at the first page and inducing it to the > > + * whole bio > > + */ > > + if (unlikely(PageWorkingset(iter->bvec->bv_page))) > > + bio_set_flag(bio, BIO_WORKINGSET); > > IIRC the feedback was that we do not need to deal with BIO_WORKINGSET > at all for direct I/O.
Yes, this hunk is incorrect. We must not use this flag for direct IO. It's only for paging IO, when you bring in the data at page->mapping + page->index. Otherwise you tell the pressure accounting code that you are paging in a thrashing page, when really you're just reading new data into a page frame that happens to be hot. (As per the other thread, bio_add_page() currently makes that same mistake for direct IO. I'm fixing that.)
