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review.shift-gmbh.com / SHIFTPHONES / kernel / shift / mainline / 6e12c5b7d418afe6670097dd6d214c55a6592c5a
commit6e12c5b7d418afe6670097dd6d214c55a6592c5a[log] [tgz]
authorMinchan Kim <minchan@kernel.org>Thu Mar 18 09:56:10 2021 -0700
committerMinchan Kim <minchan@google.com>Fri Apr 30 09:13:34 2021 -0700
tree448683462d3b6d1ba37d7981202b2dd62ca387a4
parent926cf69af5f28f3bea38651bad498bd294ea80f4 [diff]
ANDROID: mm: introduce page_pinner

For CMA allocation, it's really critical to migrate a page but
sometimes it fails. One of the reasons is some driver holds a
page refcount for a long time so VM couldn't migrate the page
at that time.

The concern here is there is no way to find the who hold the
refcount of the page effectively. This patch introduces feature
to keep tracking page's pinner. All get_page sites are vulnerable
to pin a page for a long time but the cost to keep track it would
be significat since get_page is the most frequent kernel operation.
Furthermore, the page could be not user page but kernel page which
is not related to the page migration failure. So, this patch keeps
tracking only get_user_pages/follow_page with (FOLL_GET|PIN friends
because they are the very common APIs to pin user pages which could
cause migration failure and the less frequent than get_page so
runtime cost wouldn't be that big but could cover many cases
effectively.

This patch also introduces put_user_page API. It aims for attributing
"the pinner releases the page from now on" while it release the
page refcount. Thus, any user of get_user_pages/follow_page(FOLL_GET)
must use put_user_page as pair of those functions. Otherwise,
page_pinner will treat them long term pinner as false postive but
nothing should affect stability.

* $debugfs/page_pinner/threshold

It indicates threshold(microsecond) to flag long term pinning.
It's configurable(Default is 300000us). Once you write new value
to the threshold, old data will clear.

* $debugfs/page_pinner/longterm_pinner

It shows call sites where the duration of pinning was greater than
the threshold. Internally, it uses a static array to keep 4096
elements and overwrites old ones once overflow happens. Therefore,
you could lose some information.

example)
Page pinned ts 76953865787 us count 1
PFN 9856945 Block 9625 type Movable Flags 0x8000000000080014(uptodate|lru|swapbacked)
 __set_page_pinner+0x34/0xcc
 try_grab_page+0x19c/0x1a0
 follow_page_pte+0x1c0/0x33c
 follow_page_mask+0xc0/0xc8
 __get_user_pages+0x178/0x414
 __gup_longterm_locked+0x80/0x148
 internal_get_user_pages_fast+0x140/0x174
 pin_user_pages_fast+0x24/0x40
 CCC
 BBB
 AAA
 __arm64_sys_ioctl+0x94/0xd0
 el0_svc_common+0xa4/0x180
 do_el0_svc+0x28/0x88
 el0_svc+0x14/0x24

note: page_pinner doesn't guarantee attributing/unattributing are
atomic if they happen at the same time. It's just best effort so
false-positive could happen.

Bug: 183414571
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Minchan Kim <minchan@google.com>
Change-Id: Ife37ec360eef993d390b9c131732218a4dfd2f04
10 files changed
tree: 448683462d3b6d1ba37d7981202b2dd62ca387a4
  1. android/
  2. arch/
  3. block/
  4. certs/
  5. crypto/
  6. Documentation/
  7. drivers/
  8. fs/
  9. include/
  10. init/
  11. ipc/
  12. kernel/
  13. lib/
  14. LICENSES/
  15. mm/
  16. net/
  17. samples/
  18. scripts/
  19. security/
  20. sound/
  21. tools/
  22. usr/
  23. virt/
  24. .clang-format
  25. .cocciconfig
  26. .get_maintainer.ignore
  27. .gitattributes
  28. .gitignore
  29. .mailmap
  30. build.config.aarch64
  31. build.config.allmodconfig
  32. build.config.allmodconfig.aarch64
  33. build.config.allmodconfig.arm
  34. build.config.allmodconfig.x86_64
  35. build.config.amlogic
  36. build.config.arm
  37. build.config.common
  38. build.config.db845c
  39. build.config.gki
  40. build.config.gki-debug.aarch64
  41. build.config.gki-debug.x86_64
  42. build.config.gki.aarch64
  43. build.config.gki.x86_64
  44. build.config.gki_kasan
  45. build.config.gki_kasan.aarch64
  46. build.config.gki_kasan.x86_64
  47. build.config.gki_kprobes
  48. build.config.gki_kprobes.aarch64
  49. build.config.gki_kprobes.x86_64
  50. build.config.hikey960
  51. build.config.khwasan
  52. build.config.x86_64
  53. COPYING
  54. CREDITS
  55. Kbuild
  56. Kconfig
  57. MAINTAINERS
  58. Makefile
  59. OWNERS
  60. README
  61. README.md
README.md

How do I submit patches to Android Common Kernels

  1. BEST: Make all of your changes to upstream Linux. If appropriate, backport to the stable releases. These patches will be merged automatically in the corresponding common kernels. If the patch is already in upstream Linux, post a backport of the patch that conforms to the patch requirements below.

    • Do not send patches upstream that contain only symbol exports. To be considered for upstream Linux, additions of EXPORT_SYMBOL_GPL() require an in-tree modular driver that uses the symbol -- so include the new driver or changes to an existing driver in the same patchset as the export.
    • When sending patches upstream, the commit message must contain a clear case for why the patch is needed and beneficial to the community. Enabling out-of-tree drivers or functionality is not not a persuasive case.

  2. LESS GOOD: Develop your patches out-of-tree (from an upstream Linux point-of-view). Unless these are fixing an Android-specific bug, these are very unlikely to be accepted unless they have been coordinated with kernel-team@android.com. If you want to proceed, post a patch that conforms to the patch requirements below.

Common Kernel patch requirements

  • All patches must conform to the Linux kernel coding standards and pass script/checkpatch.pl
  • Patches shall not break gki_defconfig or allmodconfig builds for arm, arm64, x86, x86_64 architectures (see https://source.android.com/setup/build/building-kernels)
  • If the patch is not merged from an upstream branch, the subject must be tagged with the type of patch: UPSTREAM:, BACKPORT:, FROMGIT:, FROMLIST:, or ANDROID:.
  • All patches must have a Change-Id: tag (see https://gerrit-review.googlesource.com/Documentation/user-changeid.html)
  • If an Android bug has been assigned, there must be a Bug: tag.
  • All patches must have a Signed-off-by: tag by the author and the submitter

Additional requirements are listed below based on patch type

Requirements for backports from mainline Linux: UPSTREAM:, BACKPORT:

  • If the patch is a cherry-pick from Linux mainline with no changes at all
    • tag the patch subject with UPSTREAM:.
    • add upstream commit information with a (cherry picked from commit ...) line
    • Example:
      • if the upstream commit message is
        important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>
  • then Joe Smith would upload the patch for the common kernel as
        UPSTREAM: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        (cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
        Signed-off-by: Joe Smith <joe.smith@foo.org>
  • If the patch requires any changes from the upstream version, tag the patch with BACKPORT: instead of UPSTREAM:.
    • use the same tags as UPSTREAM:
    • add comments about the changes under the (cherry picked from commit ...) line
    • Example:
        BACKPORT: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        (cherry picked from commit c31e73121f4c1ec41143423ac6ce3ce6dafdcec1)
        [joe: Resolved minor conflict in drivers/foo/bar.c ]
        Signed-off-by: Joe Smith <joe.smith@foo.org>

Requirements for other backports: FROMGIT:, FROMLIST:,

  • If the patch has been merged into an upstream maintainer tree, but has not yet been merged into Linux mainline
    • tag the patch subject with FROMGIT:
    • add info on where the patch came from as (cherry picked from commit <sha1> <repo> <branch>). This must be a stable maintainer branch (not rebased, so don't use linux-next for example).
    • if changes were required, use BACKPORT: FROMGIT:
    • Example:
      • if the commit message in the maintainer tree is
        important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>
  • then Joe Smith would upload the patch for the common kernel as
        FROMGIT: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        (cherry picked from commit 878a2fd9de10b03d11d2f622250285c7e63deace
         https://git.kernel.org/pub/scm/linux/kernel/git/foo/bar.git test-branch)
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        Signed-off-by: Joe Smith <joe.smith@foo.org>
  • If the patch has been submitted to LKML, but not accepted into any maintainer tree
    • tag the patch subject with FROMLIST:
    • add a Link: tag with a link to the submittal on lore.kernel.org
    • add a Bug: tag with the Android bug (required for patches not accepted into a maintainer tree)
    • if changes were required, use BACKPORT: FROMLIST:
    • Example:
        FROMLIST: important patch from upstream

        This is the detailed description of the important patch

        Signed-off-by: Fred Jones <fred.jones@foo.org>

        Bug: 135791357
        Link: https://lore.kernel.org/lkml/20190619171517.GA17557@someone.com/
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        Signed-off-by: Joe Smith <joe.smith@foo.org>

Requirements for Android-specific patches: ANDROID:

  • If the patch is fixing a bug to Android-specific code
    • tag the patch subject with ANDROID:
    • add a Fixes: tag that cites the patch with the bug
    • Example:
        ANDROID: fix android-specific bug in foobar.c

        This is the detailed description of the important fix

        Fixes: 1234abcd2468 ("foobar: add cool feature")
        Change-Id: I4caaaa566ea080fa148c5e768bb1a0b6f7201c01
        Signed-off-by: Joe Smith <joe.smith@foo.org>
  • If the patch is a new feature
    • tag the patch subject with ANDROID:
    • add a Bug: tag with the Android bug (required for android-specific features)