Messages in this thread | | | Date | Wed, 8 Nov 2023 10:01:19 +0800 | Subject | Re: [PATCH v2] kpageflags: respect folio head-page flag placement | From | Kefeng Wang <> |
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On 2023/11/7 23:34, Gregory Price wrote: > 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@huawei.com/ >> >> Thanks. > > looks like we were noticing the same thing. I haven't done any further > work, got caught up in another project.
Yes, I see your "Node Weights and Weighted Interleave", this is an interesting topic, we need some easy and efficient way to use tiered memory.
> > 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@casper.infradead.org/ > > 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.
If you don't mind, I maybe try to convert it in my changes.
Thanks. > > ~Gregory
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