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 uXjdZNNw 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Wang wrote: > > +static enum madvise_lock_mode get_lock_mode(struct madvise_behavior *madv_behavior) > > { > > + int behavior = madv_behavior->behavior; > > + > > if (is_memory_failure(behavior)) > > - return 0; > > + return MADVISE_NO_LOCK; > > - if (madvise_need_mmap_write(behavior)) { > > + switch (behavior) { > > + case MADV_REMOVE: > > + case MADV_WILLNEED: > > + case MADV_COLD: > > + case MADV_PAGEOUT: > > + case MADV_FREE: > > + case MADV_POPULATE_READ: > > + case MADV_POPULATE_WRITE: > > + case MADV_COLLAPSE: > > + case MADV_GUARD_INSTALL: > > + case MADV_GUARD_REMOVE: > > + return MADVISE_MMAP_READ_LOCK; > > + case MADV_DONTNEED: > > + case MADV_DONTNEED_LOCKED: > > + return MADVISE_VMA_READ_LOCK; > > I have a question, we will try per-vma lock for dontneed, > but there is a mmap_assert_locked() during madvise_dontneed_free(), Hmm, this is only in the THP PUD huge case, and MADV_FREE is only valid for anonymous memory, and I think only DAX can have some weird THP PUD case. So I don't think we can hit this. In any event, I think this mmap_assert_locked() is mistaken, as we should only need a VMA lock here. So we could replace with a: if (!rwsem_is_locked(&tlb->mm->mmap_lock)) vma_assert_locked(vma); ? > > madvise_dontneed_free > madvise_dontneed_single_vma > zap_page_range_single_batched > unmap_single_vma > unmap_page_range > zap_pud_range > mmap_assert_locked > > We could fix it by passing the lock_mode into zap_detial and then check > the right lock here, but I'm not sure whether it is safe to zap page > only with vma lock? It's fine to zap with the VMA lock. You need only hold the VMA stable which a VMA lock achieves. See https://docs.kernel.org/mm/process_addrs.html > > And another about 4f8ba33bbdfc （"mm: madvise: use per_vma lock > for MADV_FREE"）, it called walk_page_range_vma() in > madvise_free_single_vma(), but from link[1] and 5631da56c9a8 > ("fs/proc/task_mmu: read proc/pid/maps under per-vma lock"), it saids > > "Note that similar approach would not work for /proc/pid/smaps > reading as it also walks the page table and that's not RCU-safe" > > We could use walk_page_range_vma() instead of walk_page_range() in > smap_gather_stats(), and same question, why 4f8ba33bbdfc(for MADV_FREEE) > is safe but not for show_numa_map()/show_smap()? We only use walk_page_range() there in case 4 listed in show_smaps_rollup() where the mmap lock is dropped on contention. > > Thanks. > > [1] https://lkml.kernel.org/r/20250719182854.3166724-1-surenb@google.com AFAICT That's referring to a previous approach that tried to walk /proc/$pid/swaps under RCU _alone_ without VMA locks. This is not safe as page tables can be yanked from under you not under RCU. Cheers, Lorenzo