Sorry for the delay (holidays etc.) On Tue, Jul 09, 2024 at 10:42:58AM -0700, Yang Shi wrote: > On 7/4/24 6:44 AM, Catalin Marinas wrote: > > It might be better to convert those page flag checks to only happen on > > the head page. My stashed changes from over a year ago (before we had > > more folio conversions) below. However, as I mentioned, I got stuck on > > folio_copy() which also does a cond_resched() between copy_highpage(). > > We can have the page flags set for head only for hugetlb page. For > copy_highpage(), we should be able to do something like the below: > > if page_is_head && page_is_hugetlb && page_has_mte_tagged > set page_mte_tagged flags > copy tags for all sub pages > else // <-- tail page or non-hugetlb page > current copy_highpage implementation Ah, so you want in the first copy_highpage() for the head page to populate the tags for the tail pages. I guess this would work. > The hugetlb folio can't go away under us since migration path should pin it > so the status of folio is stable. The preemption caused by cond_resched() > should be fine too due to the pin and the page table entry keeps being > migration entry until migration is done, so every one should just see > migration entry and wait for migration is done. Yeah, I don't see those pages going away, otherwise folio_copy() would corrupt data. > The other concerned user of copy_highpage() is uprobe, but it also pins the > page then doing copy and it is called with holding write mmap_lock. > > IIUC, it should work if I don't miss something. This also should have no > impact on HVO. The overhead for other users of copy_highpage() should be > also acceptable. I also think so. We also have the copy_user_highpage() on arm64 that calls copy_highpage() but I think that's also safe. -- Catalin
