[PATCH v2 0/5] mm: A few cleanup patches around zap, shmem and uffd

Peter Xu
2021-09-02T20:17:28Z

[Based on tag v5.14, but it should still apply to -mm too. If not, I can
repost anytime]

Hugh,

So I found one thing that I feel like a bug of commit 22061a1ffabdb9c3, but I'm
not sure. If that's the case, patch 5 of this series may be the fix for it.

The problem is unmap_mapping_page() in current tree is calling
unmap_mapping_range_tree() with a details pointer, while by default when detail
pointer is specified, it means "we want to skip zapping swap entries".

I didn't mention this in v1 simply because I thought it was fine, e.g., swap
entry won't be kept in shmem ptes so skipped is okay (it is never okay with
shmem uffd-wp but uffd-wp code is not landed yet). However I just remembered
there could also be e.g. shmem migration entries if I'm not wrong. From that
pov, skipping swap entries for unmap_mapping_page() seems wrong. Would you
please help check?

It'll be great if you can comment on patch 1 too, to see whether that's okay
and what I could have been missing there (e.g., if you have other concern on
breaking stuff, I'll be happy to test).

v2:
- Patch "mm: Clear vmf->pte after pte_unmap_same() returns"
- Remove one comment [David]
- Collect r-b for patch 2/3
- Rewrite the last two patches to drop ZAP_FLAG_CHECK_MAPPING, dropping
Alistair's r-b on patch 5 because it changed [David, Matthew]

===== v1 cover letter =====

I picked up these patches from uffd-wp v5 series here:

https://lore.kernel.org/lkml/20210715201422.211004-1-peterx@redhat.com/

IMHO all of them are very nice cleanups to existing code already, they're all
small and self-contained. They'll be needed by uffd-wp coming series. I would
appreciate if they can be accepted earlier, so as to not carry them over always
with the uffd-wp series.

I removed some CC from the uffd-wp v5 series to reduce the noise, and added a
few more into it.

Reviews are greatly welcomed, thanks.

Peter Xu (5):
mm/shmem: Unconditionally set pte dirty in mfill_atomic_install_pte
mm: Clear vmf->pte after pte_unmap_same() returns
mm: Drop first_index/last_index in zap_details
mm: Add zap_skip_check_mapping() helper
mm: Add ZAP_FLAG_SKIP_SWAP and zap_flags

include/linux/mm.h | 33 ++++++++++++++++++--
mm/memory.c | 76 +++++++++++++++++++---------------------------
mm/shmem.c | 1 -
mm/userfaultfd.c | 3 +-
4 files changed, 62 insertions(+), 51 deletions(-)

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2.31.1