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ra->prev_pos tracks the last visited byte in the previous read request. It is used to check whether it is sequential read in ondemand_readahead and thus affects the readahead window. After commit06c0444290("mm/filemap.c: generic_file_buffered_read() now uses find_get_pages_contig"), update logic of prev_pos is changed. It updates prev_pos after each return from filemap_get_pages(). But the read request from user may be not fully completed at this point. The updated prev_pos impacts the subsequent readahead window. The real problem is performance drop of fsck_msdos between linux-5.4 and linux-5.15(also linux-6.4). Comparing to linux-5.4,It spends about 110% time and read 140% pages. The read pattern of fsck_msdos is not fully sequential. Simplified read pattern of fsck_msdos likes below: 1.read at page offset 0xa,size 0x1000 2.read at other page offset like 0x20,size 0x1000 3.read at page offset 0xa,size 0x4000 4.read at page offset 0xe,size 0x1000 Here is the read status on linux-6.4: 1.after read at page offset 0xa,size 0x1000 ->page ofs 0xa go into pagecache 2.after read at page offset 0x20,size 0x1000 ->page ofs 0x20 go into pagecache 3.read at page offset 0xa,size 0x4000 ->filemap_get_pages read ofs 0xa from pagecache and returns ->prev_pos is updated to 0xb and goto next loop ->filemap_get_pages tends to read ofs 0xb,size 0x3000 ->initial_readahead case in ondemand_readahead since prev_pos is the same as request ofs. ->read 8 pages while async size is 5 pages (PageReadahead flag at page 0xe) 4.read at page offset 0xe,size 0x1000 ->hit page 0xe with PageReadahead flag set,double the ra_size. read 16 pages while async size is 16 pages Now it reads 24 pages while actually uses 5 pages on linux-5.4: 1.the same as 6.4 2.the same as 6.4 3.read at page offset 0xa,size 0x4000 ->read ofs 0xa from pagecache ->read ofs 0xb,size 0x3000 using page_cache_sync_readahead read 3 pages ->prev_pos is updated to 0xd before generic_file_buffered_read returns 4.read at page offset 0xe,size 0x1000 ->initial_readahead case in ondemand_readahead since request ofs-prev_pos==1 ->read 4 pages while async size is 3 pages Now it reads 7 pages while actually uses 5 pages. In above demo, the initial_readahead case is triggered by offset of user request on linux-5.4. While it may be triggered by update logic of prev_pos on linux-6.4. To fix the performance drop, update prev_pos after finishing one read request. Link: https://lkml.kernel.org/r/20230628110220.120134-1-haibo.li@mediatek.com Change-Id: I7c9c9f8630df580120498a38ec7543ba20931201 Signed-off-by: Haibo Li <haibo.li@mediatek.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Matthias Brugger <matthias.bgg@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Bug: 298557577 (cherry picked from commitf04d16ee3a) Change-Id: Ie2adb86d5642f01465d5c7ffef71cc6964598afc Signed-off-by: Lecopzer Chen <lecopzer.chen@mediatek.com>
How do I submit patches to Android Common Kernels
-
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.
- Do not send patches upstream that contain only symbol exports. To be considered for upstream Linux,
additions of
-
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
scripts/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:, orANDROID:. - 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
- tag the patch subject with
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 ofUPSTREAM:.- use the same tags as
UPSTREAM: - add comments about the changes under the
(cherry picked from commit ...)line - Example:
- use the same tags as
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 uselinux-nextfor example). - if changes were required, use
BACKPORT: FROMGIT: - Example:
- if the commit message in the maintainer tree is
- tag the patch subject with
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:
- tag the patch subject with
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:
- tag the patch subject with
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)
- tag the patch subject with