On Tue, Nov 07, 2023 at 09:03:53AM +0800, Kefeng Wang wrote: > > > On 2023/10/31 12:34, Gregory Price wrote: > > On Tue, Oct 31, 2023 at 09:13:44AM +0000, Matthew Wilcox wrote: > > > On Mon, Oct 30, 2023 at 07:41:23PM -0400, Gregory Price wrote: > > > > On Mon, Oct 30, 2023 at 11:22:18PM +0000, Matthew Wilcox wrote: > > > > > On Mon, Oct 30, 2023 at 02:00:05PM -0400, Gregory Price wrote: > > > > > > kpageflags reads page-flags directly from the page, even when the > > > > > > respective flag is only updated on the headpage of a folio. > > > > > > > > > > > > Update bitchecks to use PAGEFLAG() interfaces to check folio for the > > > > > > referenced, dirty, lru, active, and unevictable bits. > > > > > > > > > > But uptodate, writeback and reclaim (amongst others) are also defined > > > > > only on the head page. > > > > > > > > > > > > > Ah yes i was only looking at the things defined w/ PAGEFLAG defines in > > > > page-flags.h. I'll give it full once over can collect them all, my bad. > > > > > > > > (also i forgot to update my commit message) > > > > > > > > Quick question here since i have your attention: any recommendation on > > > > what to do for ONLY_HEAD flags? If the provided page is not the head, > > > > should the flag report 0... or whatever the head says? > > > > > > Thinking about it some more, really almost all flags are per-folio, not > > > per-page. The only exceptions are HWPoison and AnonExclusive. So > > > probably the right way to do this is to make k = folio->flags, and > > > then just change a few places rather than changing all the places that > > > test 'k'. > > > > Funny enough that's what i originally did but was confident it was > > correct so walked it back. I'll take another crack at it. > > Hi Gregory, any update? > I changed stable_page_flags[1] when try to remove page idle wrapper, > Matthew pointed it will conflict with this, I could redo my patch > based on your new version:) > > [1]https://lore.kernel.org/linux-mm/20231103072906.2000381-5-wangkefeng.wang@xxxxxxxxxx/ > > Thanks. looks like we were noticing the same thing. I haven't done any further work, got caught up in another project. Matthew last pointed out: "probably the right way to do this is to make k = folio->flags, and then just change a few places rather than changing all the places that test 'k'." https://lore.kernel.org/linux-mm/ZUDFSEvpxxoGWmdG@xxxxxxxxxxxxxxxxxxxx/ I took a quick look, and the only thing I'm not confident about is that some flags are stored in the head page, and some are stored on the second page. /* Which page is the flag stored in */ #define FOLIO_PF_ANY 0 #define FOLIO_PF_HEAD 0 #define FOLIO_PF_ONLY_HEAD 0 #define FOLIO_PF_NO_TAIL 0 #define FOLIO_PF_NO_COMPOUND 0 #define FOLIO_PF_SECOND 1 There's only a handful, so yeah the best way is probably to go ahead and swap k = page->flags for k = *folio_flags(folio, 0) and then handle the couple of outliars. ~Gregory
