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. > > > 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 >>>> >> >>
