Re: [RFC PATCH v5 00/14] mm: mglru: fix swappiness behavior

[Kairui Song]

On Fri, Oct 23, 2026 at 6:02 AM Barry Song (Xiaomi) <baohua@xxxxxxxxxx> wrote:
>
> Classic LRU respects swappiness, while MGLRU only partially honors it
> when selecting the scan type, resulting in a much smaller overall
> impact.
>
> For example, when building the kernel in a memcg limited to 1024 MB
> of memory, with swappiness=200, CLRU barely scans or reclaims file
> pages, while MGLRU still reclaims a significant number of them.
> Similarly, with swappiness=1, MGLRU does not reclaim as many file
> pages as expected for such an extreme swappiness value:
>
> pgsteal_file
> swappiness   CLRU          MGLRU(no patches)
> 1            5,894,538     756,589
> 36           799,998       497,282
> 71           548,331       415,612
> 106          407,012       383,814
> 141          253,737       354,249
> 176          189,003       347,805
> 200          0             346,078
>
> pgsteal_anon
> swappiness   CLRU          MGLRU(no patches)
> 1            3,962,404     2,768,654
> 36           2,830,250     2,976,260
> 71           3,121,386     3,142,954
> 106          3,521,720     3,382,383
> 141          3,504,471     2,970,859
> 176          3,592,335     3,163,130
> 200          14,095,617    3,209,132
>
> pgscan_file
> swappiness   CLRU          MGLRU(no patches)
> 1            10,270,808    886,997
> 36           1,010,341     569,036
> 71           656,136       490,972
> 106          460,326       436,042
> 141          295,184       403,132
> 176          235,147       390,358
> 200          0             398,363
>
> pgscan_anon
> swappiness   CLRU          MGLRU(no patches)
> 1            19,341,957    5,960,884
> 36           17,530,774    6,394,951
> 71           18,624,264    6,673,569
> 106          20,088,558    6,976,364
> 141          19,686,813    6,206,580
> 176          20,936,177    6,344,854
> 200          45,313,873    6,295,581
>
> refault_file
> swappiness   CLRU          MGLRU(no patches)
> 1            5,795,115     678,254
> 36           720,877       419,659
> 71           469,270       338,518
> 106          331,584       308,983
> 141          174,509       277,375
> 176          113,352       272,390
> 200          0             269,349
>
> refault_anon
> swappiness   CLRU          MGLRU(no patches)
> 1            738,618       578,308
> 36           451,410       665,723
> 71           514,961       657,870
> 106          633,161       786,893
> 141          648,640       662,673
> 176          668,779       708,969
> 200          4,816,312     672,514

Hi Barry,

Thanks for pushing this series forward!

One nit pick so far is the test data seems redundant with the one
below, maybe we can just keep one of them.

> This model also allows scanning and reclaiming from the two youngest
> generations, including the youngest generation itself. This can help
> resolve OOM situations[1] and reduce the need for aging.

Right, the OOM reproducer is demostrated here previously:
https://lore.kernel.org/all/20260318-mglru-reclaim-v1-0-2c46f9eb0508@xxxxxxxxxxx/

That series is merged at V7:
https://lore.kernel.org/linux-mm/20260428-mglru-reclaim-v7-0-02fabb92dc43@xxxxxxxxxxx/

The problem is largely eased as described, but it isn't 100% fixed at
that time. It will still go OOM with higher pressure. So before this
series, I could still see OOM after hundreds of loops. And problem is
gone after the fixing patch in this series. Unfortunately it's very
hard to reproduce and that reproducer is the best I have so far.

>
> Patch 9 from Barry fixes a cold/hot inversion exacerbated by patches
> 1–8 (which also exists in mainline) and improves reclaim efficiency.
>
> Patches 10-13 from Gaofei and Barry optimize aging based on folio
> distribution imbalance and improve reclaim behavior at extreme
> swappiness values such as 1 and 200.
>
> Patch 14 from Bo Zhang addresses the GFP_NOIO issue in MGLRU.
>
> After the patchset, the results track CLRU across the full swappiness
> range (see table below), with more file scanning at low swappiness
> and more anon scanning at high swappiness.
>
> pgsteal_file
> swappiness   CLRU          MGLRU         MGLRU+patches
> 1            5,894,538     756,589       7,394,183
> 36           799,998       497,282       526,176
> 71           548,331       415,612       433,353
> 106          407,012       383,814       347,647
> 141          253,737       354,249       314,437
> 176          189,003       347,805       261,677
> 200          0             346,078       188
>
> pgsteal_anon
> swappiness   CLRU          MGLRU         MGLRU+patches
> 1            3,962,404     2,768,654     5,362,153
> 36           2,830,250     2,976,260     2,736,749
> 71           3,121,386     3,142,954     3,246,589
> 106          3,521,720     3,382,383     3,074,851
> 141          3,504,471     2,970,859     3,178,409
> 176          3,592,335     3,163,130     3,650,544
> 200          14,095,617    3,209,132     14,538,399
>
> pgscan_file
> swappiness   CLRU          MGLRU         MGLRU+patches
> 1            10,270,808    886,997       16,246,260
> 36           1,010,341     569,036       614,389
> 71           656,136       490,972       484,769
> 106          460,326       436,042       367,969
> 141          295,184       403,132       328,943
> 176          235,147       390,358       268,142
> 200          0             398,363       188
>
> pgscan_anon
> swappiness   CLRU          MGLRU         MGLRU+patches
> 1            19,341,957    5,960,884     7,646,122
> 36           17,530,774    6,394,951     5,914,405
> 71           18,624,264    6,673,569     7,167,762
> 106          20,088,558    6,976,364     7,821,921
> 141          19,686,813    6,206,580     8,495,970
> 176          20,936,177    6,344,854     10,585,375
> 200          45,313,873    6,295,581     30,313,342
>
> refault_file
> swappiness   CLRU          MGLRU         MGLRU+patches
> 1            5,795,115     678,254       7,315,064
> 36           720,877       419,659       448,199
> 71           469,270       338,518       355,269
> 106          331,584       308,983       270,736
> 141          174,509       277,375       237,643
> 176          113,352       272,390       184,908
> 200          0             269,349       102
>
> refault_anon
> swappiness   CLRU          MGLRU         MGLRU+patches
> 1            738,618       578,308       1,383,725
> 36           451,410       665,723       543,071
> 71           514,961       657,870       683,874
> 106          633,161       786,893       669,716
> 141          648,640       662,673       719,231
> 176          668,779       708,969       901,918
> 200          4,816,312     672,514       5,511,787

Right, that's really nice result. Do you have system time or
performance readings? BTW for the performance reading I think we can
focus on the 36 - 176 range. If a user asks for extreme bias towards
anon/file, they strongly favor reclaim priority over throughput, and
the behavior is arguable at that point.