On 8/2/2023 8:49 PM, Ryan Roberts wrote: > On 02/08/2023 13:42, Yin, Fengwei wrote: >> >> >> On 8/2/2023 8:40 PM, Ryan Roberts wrote: >>> On 02/08/2023 13:35, Yin, Fengwei wrote: >>>> >>>> >>>> On 8/2/2023 6:27 PM, Ryan Roberts wrote: >>>>> On 28/07/2023 17:13, Yin Fengwei wrote: >>>>>> In madvise_cold_or_pageout_pte_range() and madvise_free_pte_range(), >>>>>> folio_mapcount() is used to check whether the folio is shared. But it's >>>>>> not correct as folio_mapcount() returns total mapcount of large folio. >>>>>> >>>>>> Use folio_estimated_sharers() here as the estimated number is enough. >>>>>> >>>>>> Yin Fengwei (2): >>>>>> madvise: don't use mapcount() against large folio for sharing check >>>>>> madvise: don't use mapcount() against large folio for sharing check >>>>>> >>>>>> mm/huge_memory.c | 2 +- >>>>>> mm/madvise.c | 6 +++--- >>>>>> 2 files changed, 4 insertions(+), 4 deletions(-) >>>>>> >>>>> >>>>> As a set of fixes, I agree this is definitely an improvement, so: >>>>> >>>>> Reviewed-By: Ryan Roberts >>>> Thanks. >>>> >>>>> >>>>> >>>>> But I have a couple of comments around further improvements; >>>>> >>>>> Once we have the scheme that David is working on to be able to provide precise >>>>> exclusive vs shared info, we will probably want to move to that. Although that >>>>> scheme will need access to the mm_struct of a process known to be mapping the >>>>> folio. We have that info, but its not passed to folio_estimated_sharers() so we >>>>> can't just reimplement folio_estimated_sharers() - we will need to rework these >>>>> call sites again. >>>> Yes. This could be extra work. Maybe should delay till David's work is done. >>> >>> What you have is definitely an improvement over what was there before. And is >>> probably the best we can do without David's scheme. So I wouldn't delay this. >>> Just pointing out that we will be able to make it even better later on (if >>> David's stuff goes in). >> Yes. I agree that we should wait for David's work ready and do fix based on that. > > I was suggesting the opposite - not waiting. Then we can do separate improvement > later. Let's wait for David's work ready. Otherwise, some other similar fix could be submitted. Unfortunately, we can't build folio_estimated_sharers() based on folio_maybe_mapped_shared() because latter one requires the extra parameter. Regards Yin, Fengwei > >> >> >> Regards >> Yin, Fengwei >> >>> >>>> >>>>> >>>>> Given the aspiration for most of the memory to be large folios going forwards, >>>>> wouldn't it be better to avoid splitting the large folio where the large folio >>>>> is mapped entirely within the range of the madvise operation? Sorry if this has >>>>> already been discussed and decided against - I didn't follow the RFC too >>>>> closely. Or perhaps you plan to do this as a follow up? >>>> Yes. We are on same page. RFC patchset did that. But there are some other opens >>>> on the RFC. So I tried to submit this part of change which is bug fix. The other >>>> thing left in RFC is optimization (avoid split large folio if we can). >>>> >>>> >>>> Regards >>>> Yin, Fengwei >>>> >>>>> >>>>> Thanks, >>>>> Ryan >>>>> >>> >>> >
