mm/vmscan.c | 332 ++++++++++++++++++++++++++---------------------------------- 1 file changed, 143 insertions(+), 189 deletions(-)
This series is based on mm-new.
This series cleans up and slightly improves MGLRU's reclaim loop and
dirty writeback handling. As a result, we can see an up to ~30% increase
in some workloads like MongoDB with YCSB and a huge decrease in file
refault, no swap involved. Other common benchmarks have no regression,
and LOC is reduced, with less unexpected OOM, too.
Some of the problems were found in our production environment, and
others were mostly exposed while stress testing during the development
of the LSM/MM/BPF topic on improving MGLRU [1]. This series cleans up
the code base and fixes several performance issues, preparing for
further work.
MGLRU's reclaim loop is a bit complex, and hence these problems are
somehow related to each other. The aging, scan number calculation, and
reclaim loop are coupled together, and the dirty folio handling logic is
quite different, making the reclaim loop hard to follow and the dirty
flush ineffective.
This series slightly cleans up and improves these issues using a scan
budget by calculating the number of folios to scan at the beginning of
the loop, and decouples aging from the reclaim calculation helpers.
Then, move the dirty flush logic inside the reclaim loop so it can kick
in more effectively. These issues are somehow related, and this series
handles them and improves MGLRU reclaim in many ways.
Test results: All tests are done on a 48c96t NUMA machine with 2 nodes
and a 128G memory machine using NVME as storage.
MongoDB
=======
Running YCSB workloadb [2] (recordcount:20000000 operationcount:6000000,
threads:32), which does 95% read and 5% update to generate mixed read
and dirty writeback. MongoDB is set up in a 10G cgroup using Docker, and
the WiredTiger cache size is set to 4.5G, using NVME as storage.
Not using SWAP.
Before:
Throughput(ops/sec): 62485.02962831822
AverageLatency(us): 500.9746963330107
pgpgin 159347462
pgpgout 5413332
workingset_refault_anon 0
workingset_refault_file 34522071
After:
Throughput(ops/sec): 79760.71784646061 (+27.6%, higher is better)
AverageLatency(us): 391.25169970043726 (-21.9%, lower is better)
pgpgin 111093923 (-30.3%, lower is better)
pgpgout 5437456
workingset_refault_anon 0
workingset_refault_file 19566366 (-43.3%, lower is better)
We can see a significant performance improvement after this series.
The test is done on NVME and the performance gap would be even larger
for slow devices, such as HDD or network storage. We observed over
100% gain for some workloads with slow IO.
Chrome & Node.js [3]
====================
Using Yu Zhao's test script [3], testing on a x86_64 NUMA machine with 2
nodes and 128G memory, using 256G ZRAM as swap and spawn 32 memcg 64
workers:
Before:
Total requests: 79915
Per-worker 95% CI (mean): [1233.9, 1263.5]
Per-worker stdev: 59.2
Jain's fairness: 0.997795 (1.0 = perfectly fair)
Latency:
Bucket Count Pct Cumul
[0,1)s 26859 33.61% 33.61%
[1,2)s 7818 9.78% 43.39%
[2,4)s 5532 6.92% 50.31%
[4,8)s 39706 49.69% 100.00%
After:
Total requests: 81382
Per-worker 95% CI (mean): [1241.9, 1301.3]
Per-worker stdev: 118.8
Jain's fairness: 0.991480 (1.0 = perfectly fair)
Latency:
Bucket Count Pct Cumul
[0,1)s 26696 32.80% 32.80%
[1,2)s 8745 10.75% 43.55%
[2,4)s 6865 8.44% 51.98%
[4,8)s 39076 48.02% 100.00%
Reclaim is still fair and effective, total requests number seems
slightly better.
OOM issue with aging and throttling
===================================
For the throttling OOM issue, it can be easily reproduced using dd and
cgroup limit as demonstrated in patch 14, and fixed by this series.
The aging OOM is a bit tricky, a specific reproducer can be used to
simulate what we encountered in production environment [4]:
Spawns multiple workers that keep reading the given file using mmap,
and pauses for 120ms after one file read batch. It also spawns another
set of workers that keep allocating and freeing a given size of
anonymous memory. The total memory size exceeds the memory limit
(eg. 14G anon + 8G file, which is 22G vs a 16G memcg limit).
- MGLRU disabled:
Finished 128 iterations.
- MGLRU enabled:
OOM with following info after about ~10-20 iterations:
[ 62.624130] file_anon_mix_p invoked oom-killer: gfp_mask=0xcc0(GFP_KERNEL), order=0, oom_score_adj=0
[ 62.624999] memory: usage 16777216kB, limit 16777216kB, failcnt 24460
[ 62.640200] swap: usage 0kB, limit 9007199254740988kB, failcnt 0
[ 62.640823] Memory cgroup stats for /demo:
[ 62.641017] anon 10604879872
[ 62.641941] file 6574858240
OOM occurs despite there being still evictable file folios.
- MGLRU enabled after this series:
Finished 128 iterations.
Worth noting there is another OOM related issue reported in V1 of
this series, which is tested and looking OK now [5].
MySQL:
======
Testing with innodb_buffer_pool_size=26106127360, in a 2G memcg, using
ZRAM as swap and test command:
sysbench /usr/share/sysbench/oltp_read_only.lua --mysql-db=sb \
--tables=48 --table-size=2000000 --threads=48 --time=600 run
Before: 17260.781429 tps
After this series: 17266.842857 tps
MySQL is anon folios heavy, involves writeback and file and still
looking good. Seems only noise level changes, no regression.
FIO:
====
Testing with the following command, where /mnt/ramdisk is a
64G EXT4 ramdisk, each test file is 3G, in a 10G memcg,
6 test run each:
fio --directory=/mnt/ramdisk --filename_format='test.$jobnum.img' \
--name=cached --numjobs=16 --size=3072M --buffered=1 --ioengine=mmap \
--rw=randread --norandommap --time_based \
--ramp_time=1m --runtime=5m --group_reporting
Before: 9196.481429 MB/s
After this series: 9256.105000 MB/s
Also seem only noise level changes and no regression or slightly better.
Build kernel:
=============
Build kernel test using ZRAM as swap, on top of tmpfs, in a 3G memcg
using make -j96 and defconfig, measuring system time, 12 test run each.
Before: 2589.63s
After this series: 2543.58s
Also seem only noise level changes, no regression or very slightly better.
Link: https://lore.kernel.org/linux-mm/CAMgjq7BoekNjg-Ra3C8M7=8=75su38w=HD782T5E_cxyeCeH_g@mail.gmail.com/ [1]
Link: https://github.com/brianfrankcooper/YCSB/blob/master/workloads/workloadb [2]
Link: https://lore.kernel.org/all/20221220214923.1229538-1-yuzhao@google.com/ [3]
Link: https://github.com/ryncsn/emm-test-project/tree/master/file-anon-mix-pressure [4]
Link: https://lore.kernel.org/linux-mm/acgNCzRDVmSbXrOE@KASONG-MC4/ [5]
Signed-off-by: Kairui Song <kasong@tencent.com>
---
Changes in v3:
- Don't force scan at least SWAP_CLUSTER_MAX pages for each reclaim
loop. If the LRU is too small, adjust it accordingly. Now the
multi-cgroup scan balance looked even better for tiny cgroups:
https://lore.kernel.org/linux-mm/aciejkdIHyXPNS9Y@KASONG-MC4/
- Add one patch to remove the swap constraint check in isolate_folio. In
theory, it's fine, and both stress test and performance test didn't
show any issue:
https://lore.kernel.org/linux-mm/CAMgjq7C8TCsK99p85i3QzGCwgkXscTfFB6XCUTWQOcuqwHQa2Q@mail.gmail.com/
- I reran most tests, all seem identical, so most data is kept.
Intermediate test results are dropped. I ran tests on most patches
individually, and there is no problem, but the series is getting too
long, and posting them makes it harder to read and unnecessary.
- Split previously patch 8 into two patches as suggested [ Shakeel Butt ],
also some test result is collected to support the design:
https://lore.kernel.org/linux-mm/ac44BVOvOm8lhVvj@KASONG-MC4/#t
I kept Axel's review-by since the code is identical.
- Call try_to_inc_min_seq twice to avoid stale empty gen and drop
its return argument [ Baolin Wang ]
- Move a few lines of code between patches to where they fits better,
the final result is identical [ Baolin Wang ].
- Collect tested by and update test setup [ Leno Hou ]
- Collect review by.
- Update a few commit message [ Shakeel Butt ].
- Link to v2: https://patch.msgid.link/20260329-mglru-reclaim-v2-0-b53a3678513c@tencent.com
Changes in v2:
- Rebase on top of mm-new which includes Cgroup V1 fix from
[ Baolin Wang ].
- Added dirty throttling OOM fix as patch 12, as [ Chen Ridong ]'s
review suggested that we shouldn't leave the counter and reclaim
feedback in shrink_folio_list untracked in this series.
- Add a minimal scan number of SWAP_CLUSTER_MAX limit in patch
"restructure the reclaim loop", the change is trivial but might
help avoid livelock for tiny cgroups.
- Redo the tests, most test are basically identical to before, but just
in case, since the patch also solves the throttling issue now, and
discussed with reports from CachyOS.
- Add a separate patch for variable renaming as suggested by [ Barry
Song ]. No feature change.
- Improve several comment and code issue [ Axel Rasmussen ].
- Remove no longer needed variable [ Axel Rasmussen ].
- Collect review by.
- Link to v1: https://lore.kernel.org/r/20260318-mglru-reclaim-v1-0-2c46f9eb0508@tencent.com
---
Kairui Song (14):
mm/mglru: consolidate common code for retrieving evictable size
mm/mglru: rename variables related to aging and rotation
mm/mglru: relocate the LRU scan batch limit to callers
mm/mglru: restructure the reclaim loop
mm/mglru: scan and count the exact number of folios
mm/mglru: use a smaller batch for reclaim
mm/mglru: don't abort scan immediately right after aging
mm/mglru: remove redundant swap constrained check upon isolation
mm/mglru: use the common routine for dirty/writeback reactivation
mm/mglru: simplify and improve dirty writeback handling
mm/mglru: remove no longer used reclaim argument for folio protection
mm/vmscan: remove sc->file_taken
mm/vmscan: remove sc->unqueued_dirty
mm/vmscan: unify writeback reclaim statistic and throttling
mm/vmscan.c | 332 ++++++++++++++++++++++++++----------------------------------
1 file changed, 143 insertions(+), 189 deletions(-)
---
base-commit: c17461ca3e91a3fe705685a23ad7edb58d4ee768
change-id: 20260314-mglru-reclaim-1c9d45ac57f6
Best regards,
--
Kairui Song <kasong@tencent.com>
On Thu, Apr 2, 2026 at 11:53 AM Kairui Song via B4 Relay <devnull+kasong.tencent.com@kernel.org> wrote: > > This series is based on mm-new. > > This series cleans up and slightly improves MGLRU's reclaim loop and > dirty writeback handling. As a result, we can see an up to ~30% increase > in some workloads like MongoDB with YCSB and a huge decrease in file > refault, no swap involved. Other common benchmarks have no regression, > and LOC is reduced, with less unexpected OOM, too. > > Some of the problems were found in our production environment, and > others were mostly exposed while stress testing during the development > of the LSM/MM/BPF topic on improving MGLRU [1]. This series cleans up > the code base and fixes several performance issues, preparing for > further work. > > MGLRU's reclaim loop is a bit complex, and hence these problems are > somehow related to each other. The aging, scan number calculation, and > reclaim loop are coupled together, and the dirty folio handling logic is > quite different, making the reclaim loop hard to follow and the dirty > flush ineffective. > > This series slightly cleans up and improves these issues using a scan > budget by calculating the number of folios to scan at the beginning of > the loop, and decouples aging from the reclaim calculation helpers. > Then, move the dirty flush logic inside the reclaim loop so it can kick > in more effectively. These issues are somehow related, and this series > handles them and improves MGLRU reclaim in many ways. > > Test results: All tests are done on a 48c96t NUMA machine with 2 nodes > and a 128G memory machine using NVME as storage. > > MongoDB > ======= > Running YCSB workloadb [2] (recordcount:20000000 operationcount:6000000, > threads:32), which does 95% read and 5% update to generate mixed read > and dirty writeback. MongoDB is set up in a 10G cgroup using Docker, and > the WiredTiger cache size is set to 4.5G, using NVME as storage. > > Not using SWAP. > > Before: > Throughput(ops/sec): 62485.02962831822 > AverageLatency(us): 500.9746963330107 > pgpgin 159347462 > pgpgout 5413332 > workingset_refault_anon 0 > workingset_refault_file 34522071 > > After: > Throughput(ops/sec): 79760.71784646061 (+27.6%, higher is better) > AverageLatency(us): 391.25169970043726 (-21.9%, lower is better) > pgpgin 111093923 (-30.3%, lower is better) > pgpgout 5437456 > workingset_refault_anon 0 > workingset_refault_file 19566366 (-43.3%, lower is better) > > We can see a significant performance improvement after this series. > The test is done on NVME and the performance gap would be even larger > for slow devices, such as HDD or network storage. We observed over > 100% gain for some workloads with slow IO. > > Chrome & Node.js [3] > ==================== > Using Yu Zhao's test script [3], testing on a x86_64 NUMA machine with 2 > nodes and 128G memory, using 256G ZRAM as swap and spawn 32 memcg 64 > workers: > > Before: > Total requests: 79915 > Per-worker 95% CI (mean): [1233.9, 1263.5] > Per-worker stdev: 59.2 > Jain's fairness: 0.997795 (1.0 = perfectly fair) > Latency: > Bucket Count Pct Cumul > [0,1)s 26859 33.61% 33.61% > [1,2)s 7818 9.78% 43.39% > [2,4)s 5532 6.92% 50.31% > [4,8)s 39706 49.69% 100.00% > > After: > Total requests: 81382 > Per-worker 95% CI (mean): [1241.9, 1301.3] > Per-worker stdev: 118.8 > Jain's fairness: 0.991480 (1.0 = perfectly fair) > Latency: > Bucket Count Pct Cumul > [0,1)s 26696 32.80% 32.80% > [1,2)s 8745 10.75% 43.55% > [2,4)s 6865 8.44% 51.98% > [4,8)s 39076 48.02% 100.00% > > Reclaim is still fair and effective, total requests number seems > slightly better. > > OOM issue with aging and throttling > =================================== > For the throttling OOM issue, it can be easily reproduced using dd and > cgroup limit as demonstrated in patch 14, and fixed by this series. > > The aging OOM is a bit tricky, a specific reproducer can be used to > simulate what we encountered in production environment [4]: > Spawns multiple workers that keep reading the given file using mmap, > and pauses for 120ms after one file read batch. It also spawns another > set of workers that keep allocating and freeing a given size of > anonymous memory. The total memory size exceeds the memory limit > (eg. 14G anon + 8G file, which is 22G vs a 16G memcg limit). > > - MGLRU disabled: > Finished 128 iterations. > > - MGLRU enabled: > OOM with following info after about ~10-20 iterations: > [ 62.624130] file_anon_mix_p invoked oom-killer: gfp_mask=0xcc0(GFP_KERNEL), order=0, oom_score_adj=0 > [ 62.624999] memory: usage 16777216kB, limit 16777216kB, failcnt 24460 > [ 62.640200] swap: usage 0kB, limit 9007199254740988kB, failcnt 0 > [ 62.640823] Memory cgroup stats for /demo: > [ 62.641017] anon 10604879872 > [ 62.641941] file 6574858240 > > OOM occurs despite there being still evictable file folios. > > - MGLRU enabled after this series: > Finished 128 iterations. > > Worth noting there is another OOM related issue reported in V1 of > this series, which is tested and looking OK now [5]. > > MySQL: > ====== > > Testing with innodb_buffer_pool_size=26106127360, in a 2G memcg, using > ZRAM as swap and test command: > > sysbench /usr/share/sysbench/oltp_read_only.lua --mysql-db=sb \ > --tables=48 --table-size=2000000 --threads=48 --time=600 run > > Before: 17260.781429 tps > After this series: 17266.842857 tps > > MySQL is anon folios heavy, involves writeback and file and still > looking good. Seems only noise level changes, no regression. > > FIO: > ==== > Testing with the following command, where /mnt/ramdisk is a > 64G EXT4 ramdisk, each test file is 3G, in a 10G memcg, > 6 test run each: > > fio --directory=/mnt/ramdisk --filename_format='test.$jobnum.img' \ > --name=cached --numjobs=16 --size=3072M --buffered=1 --ioengine=mmap \ > --rw=randread --norandommap --time_based \ > --ramp_time=1m --runtime=5m --group_reporting > > Before: 9196.481429 MB/s > After this series: 9256.105000 MB/s > > Also seem only noise level changes and no regression or slightly better. > > Build kernel: > ============= > Build kernel test using ZRAM as swap, on top of tmpfs, in a 3G memcg > using make -j96 and defconfig, measuring system time, 12 test run each. > > Before: 2589.63s > After this series: 2543.58s > > Also seem only noise level changes, no regression or very slightly better. > > Link: https://lore.kernel.org/linux-mm/CAMgjq7BoekNjg-Ra3C8M7=8=75su38w=HD782T5E_cxyeCeH_g@mail.gmail.com/ [1] > Link: https://github.com/brianfrankcooper/YCSB/blob/master/workloads/workloadb [2] > Link: https://lore.kernel.org/all/20221220214923.1229538-1-yuzhao@google.com/ [3] > Link: https://github.com/ryncsn/emm-test-project/tree/master/file-anon-mix-pressure [4] > Link: https://lore.kernel.org/linux-mm/acgNCzRDVmSbXrOE@KASONG-MC4/ [5] > > Signed-off-by: Kairui Song <kasong@tencent.com> > --- > Changes in v3: > - Don't force scan at least SWAP_CLUSTER_MAX pages for each reclaim > loop. If the LRU is too small, adjust it accordingly. Now the > multi-cgroup scan balance looked even better for tiny cgroups: > https://lore.kernel.org/linux-mm/aciejkdIHyXPNS9Y@KASONG-MC4/ > - Add one patch to remove the swap constraint check in isolate_folio. In > theory, it's fine, and both stress test and performance test didn't > show any issue: > https://lore.kernel.org/linux-mm/CAMgjq7C8TCsK99p85i3QzGCwgkXscTfFB6XCUTWQOcuqwHQa2Q@mail.gmail.com/ > - I reran most tests, all seem identical, so most data is kept. > Intermediate test results are dropped. I ran tests on most patches > individually, and there is no problem, but the series is getting too > long, and posting them makes it harder to read and unnecessary. > - Split previously patch 8 into two patches as suggested [ Shakeel Butt ], > also some test result is collected to support the design: > https://lore.kernel.org/linux-mm/ac44BVOvOm8lhVvj@KASONG-MC4/#t > I kept Axel's review-by since the code is identical. > - Call try_to_inc_min_seq twice to avoid stale empty gen and drop > its return argument [ Baolin Wang ] > - Move a few lines of code between patches to where they fits better, > the final result is identical [ Baolin Wang ]. > - Collect tested by and update test setup [ Leno Hou ] > - Collect review by. > - Update a few commit message [ Shakeel Butt ]. > - Link to v2: https://patch.msgid.link/20260329-mglru-reclaim-v2-0-b53a3678513c@tencent.com > > Changes in v2: > - Rebase on top of mm-new which includes Cgroup V1 fix from > [ Baolin Wang ]. > - Added dirty throttling OOM fix as patch 12, as [ Chen Ridong ]'s > review suggested that we shouldn't leave the counter and reclaim > feedback in shrink_folio_list untracked in this series. > - Add a minimal scan number of SWAP_CLUSTER_MAX limit in patch > "restructure the reclaim loop", the change is trivial but might > help avoid livelock for tiny cgroups. > - Redo the tests, most test are basically identical to before, but just > in case, since the patch also solves the throttling issue now, and > discussed with reports from CachyOS. > - Add a separate patch for variable renaming as suggested by [ Barry > Song ]. No feature change. > - Improve several comment and code issue [ Axel Rasmussen ]. > - Remove no longer needed variable [ Axel Rasmussen ]. > - Collect review by. > - Link to v1: https://lore.kernel.org/r/20260318-mglru-reclaim-v1-0-2c46f9eb0508@tencent.com > > --- > Kairui Song (14): > mm/mglru: consolidate common code for retrieving evictable size > mm/mglru: rename variables related to aging and rotation > mm/mglru: relocate the LRU scan batch limit to callers > mm/mglru: restructure the reclaim loop > mm/mglru: scan and count the exact number of folios > mm/mglru: use a smaller batch for reclaim > mm/mglru: don't abort scan immediately right after aging > mm/mglru: remove redundant swap constrained check upon isolation > mm/mglru: use the common routine for dirty/writeback reactivation > mm/mglru: simplify and improve dirty writeback handling > mm/mglru: remove no longer used reclaim argument for folio protection > mm/vmscan: remove sc->file_taken > mm/vmscan: remove sc->unqueued_dirty > mm/vmscan: unify writeback reclaim statistic and throttling I read through all of the v3 patches, for me they look ready to go. I don't see any of the remaining small optimizations as reasons not to merge at this point, there can always be some small follow up work. :) Feel free to take on any of the patches that don't already have it: Reviewed-by: Axel Rasmussen <axelrasmussen@google.com> > > mm/vmscan.c | 332 ++++++++++++++++++++++++++---------------------------------- > 1 file changed, 143 insertions(+), 189 deletions(-) > --- > base-commit: c17461ca3e91a3fe705685a23ad7edb58d4ee768 > change-id: 20260314-mglru-reclaim-1c9d45ac57f6 > > Best regards, > -- > Kairui Song <kasong@tencent.com> > >
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