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 XBguvXCS 4vtk6NRyYyOReHUmynYD0/6tGDNA21rg+UZE61c/qhFB/O5wfcvQQAFkZu506sWh95bf1fzM7CXdqGixbyqScoV6UWevy1wby9az9xyOURsDI7B7s/LJBEPq3VLJ/H81Id3H/zU4reRuErGjCWVfkIyAj3TvL6ML8yPkB395/CGpWSyFPywUQg6diXIprYJhS4yneLuEvxi9d5p66eVkmWmDfxgKrer24hxH5pd1t2m8AVF9CXKOl4V6lKzvNlebUAEBwu+aeYv977ZtZ9yYiVPjyg2FpRUEyjrnY2LXv4FqP5RJl68rox4COFRBD3css3bRlU8XCUrqYNN7o1151JGHVjoEyZLPkTggzkmXG1S2rp0BR+UUw9frDVWpS1DX9oR77hFwddehyqYJfyAPNQpOKBYk7Y6+rhM7aCu+Y530j2fPMiWfEzbt/9owC6YJwrhk0LdyiNct6/Mcjx8ZbwRm/VCiOhMI+3cObNx6Pe/NEIXM= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/7/25 13:29, Mika Penttilä wrote: > On 7/7/25 05:35, Balbir Singh wrote: >> On 7/5/25 13:17, Mika Penttilä wrote: >>>>>>> +static void migrate_vma_split_pages(struct migrate_vma *migrate, >>>>>>> + unsigned long idx, unsigned long addr, >>>>>>> + struct folio *folio) >>>>>>> +{ >>>>>>> + unsigned long i; >>>>>>> + unsigned long pfn; >>>>>>> + unsigned long flags; >>>>>>> + >>>>>>> + folio_get(folio); >>>>>>> + split_huge_pmd_address(migrate->vma, addr, true); >>>>>>> + __split_huge_page_to_list_to_order(folio_page(folio, 0), NULL, 0, true); >>>>>> We already have reference to folio, why is folio_get() needed ? >>>>>> >>>>>> Splitting the page splits pmd for anon folios, why is there split_huge_pmd_address() ? >>>>> Oh I see >>>>> + if (!isolated) >>>>> + unmap_folio(folio); >>>>> >>>>> which explains the explicit split_huge_pmd_address(migrate->vma, addr, true); >>>>> >>>>> Still, why the folio_get(folio);? >>>>> >>>>> >>>> That is for split_huge_pmd_address, when called with freeze=true, it drops the >>>> ref count on the page >>>> >>>> if (freeze) >>>> put_page(page); >>>> >>>> Balbir >>>> >>> yeah I guess you could have used the pmd_migration path in __split_huge_pmd_locked, and not use freeze because you have installed the migration pmd entry already. >>> Which brings to a bigger concern, that you do need the freeze semantics, like clear PageAnonExclusive (which may fail). I think you did not get this part >>> right in the 3/12 patch. And in this patch, you can't assume the split succeeds, which would mean you can't migrate the range at all. >>> Doing the split this late is quite problematic all in all. >>> >> Clearing PageAnonExclusive will *not* fail for device private pages from what I can see in __folio_try_share_anon_rmap(). >> Doing the split late is a requirement due to the nature of the three stage migration operation, the other side >> might fail to allocate THP sized pages and so the code needs to deal with it >> >> Balbir Singh > > Yes seems clearing PageAnonExclusive doesn't fail for device private pages in the end, > but the 3/12 patch doesn't even try to clear PageAnonExclusive with your changes afaics, > which is a separate issue. > > And __split_huge_page_to_list_to_order() (return value is not checked) can fail for out of memory. > So think you can not just assume split just works. If late split is a requirement (which I can understand is), > you should be prepared to rollback somehow the operation. > I'll add a check, rolling back is just setting up the entries to not be migrated Thanks, Balbir Singh