Message-ID: <97a9e695-487a-4428-87b7-cb8a505c9966@suse.cz>
Date: Fri, 28 Nov 2025 10:24:16 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Hongru Zhang <zhanghongru06@...il.com>, akpm@...ux-foundation.org,
 david@...nel.org
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, surenb@...gle.com,
 mhocko@...e.com, jackmanb@...gle.com, hannes@...xchg.org, ziy@...dia.com,
 lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, rppt@...nel.org,
 axelrasmussen@...gle.com, yuanchu@...gle.com, weixugc@...gle.com,
 Hongru Zhang <zhanghongru@...omi.com>
Subject: Re: [PATCH 0/3] mm: add per-migratetype counts to buddy allocator and
 optimize pagetypeinfo access

On 11/28/25 04:10, Hongru Zhang wrote:
> On mobile devices, some user-space memory management components check
> memory pressure and fragmentation status periodically or via PSI, and
> take actions such as killing processes or performing memory compaction
> based on this information.

Hm /proc/buddyinfo could be enough to determine fragmentation? Also we have
in-kernel proactive compaction these days.

> Under high load scenarios, reading /proc/pagetypeinfo causes memory
> management components or memory allocation/free paths to be blocked
> for extended periods waiting for the zone lock, leading to the following
> issues:
> 1. Long interrupt-disabled spinlocks - occasionally exceeding 10ms on Qcom
>    8750 platforms, reducing system real-time performance
> 2. Memory management components being blocked for extended periods,
>    preventing rapid acquisition of memory fragmentation information for
>    critical memory management decisions and actions
> 3. Increased latency in memory allocation and free paths due to prolonged
>    zone lock contention

It could be argued that not capturing /proc/pagetypeinfo (often) would help.
I wonder if we can find also other benefits from the counters in the kernel
itself.

Adding these migratetype counters is something that wouldn't be even
possible in the past, until the freelist migratetype hygiene was merged.
So now it should be AFAIK possible, but it's still some overhead in
relatively hot paths. I wonder if we even considered this before in the
context of migratetype hygiene? Couldn't find anything quickly.

> Changes:
> 1. Add per-migratetype counts to the buddy allocator to track free page
>    block counts for each migratetype and order
> 2. Optimize /proc/pagetypeinfo access by utilizing these per-migratetype
>    counts instead of iterating through free lists under zone lock
> 
> Performance testing shows following improvements:
> 1. /proc/pagetypeinfo access latency reduced
> 
>     +-----------------------+----------+------------+
>     |                       | no-patch | with-patch |
>     +-----------------------+----------+------------+
>     |    Just after boot    | 700.9 us |  268.6 us  |
>     +-----------------------+----------+------------+
>     | After building kernel |  28.7 ms |  269.8 us  |
>     +-----------------------+----------+------------+
> 
> 2. When /proc/pagetypeinfo is accessed concurrently, memory allocation and
>    free performance degradation is reduced compared to the previous
>    implementation
> 
> Test setup:
> - Using config-pagealloc-micro
> - Monitor set to proc-pagetypeinfo, update frequency set to 10ms
> - PAGEALLOC_ORDER_MIN=4, PAGEALLOC_ORDER_MAX=4
> 
> Without patch test results:
>                                          vanilla                vanilla
>                                        no-monitor               monitor
> Min       alloc-odr4-1        8539.00 (   0.00%)     8762.00 (  -2.61%)
> Min       alloc-odr4-2        6501.00 (   0.00%)     6683.00 (  -2.80%)
> Min       alloc-odr4-4        5537.00 (   0.00%)     5873.00 (  -6.07%)
> Min       alloc-odr4-8        5030.00 (   0.00%)     5361.00 (  -6.58%)
> Min       alloc-odr4-16       4782.00 (   0.00%)     5162.00 (  -7.95%)
> Min       alloc-odr4-32       5838.00 (   0.00%)     6499.00 ( -11.32%)
> Min       alloc-odr4-64       6565.00 (   0.00%)     7413.00 ( -12.92%)
> Min       alloc-odr4-128      6896.00 (   0.00%)     7898.00 ( -14.53%)
> Min       alloc-odr4-256      7303.00 (   0.00%)     8163.00 ( -11.78%)
> Min       alloc-odr4-512     10179.00 (   0.00%)    11985.00 ( -17.74%)
> Min       alloc-odr4-1024    11000.00 (   0.00%)    12165.00 ( -10.59%)
> Min       free-odr4-1          820.00 (   0.00%)     1230.00 ( -50.00%)
> Min       free-odr4-2          511.00 (   0.00%)      952.00 ( -86.30%)
> Min       free-odr4-4          347.00 (   0.00%)      434.00 ( -25.07%)
> Min       free-odr4-8          286.00 (   0.00%)      399.00 ( -39.51%)
> Min       free-odr4-16         250.00 (   0.00%)      405.00 ( -62.00%)
> Min       free-odr4-32         294.00 (   0.00%)      405.00 ( -37.76%)
> Min       free-odr4-64         333.00 (   0.00%)      363.00 (  -9.01%)
> Min       free-odr4-128        340.00 (   0.00%)      412.00 ( -21.18%)
> Min       free-odr4-256        339.00 (   0.00%)      329.00 (   2.95%)
> Min       free-odr4-512        361.00 (   0.00%)      409.00 ( -13.30%)
> Min       free-odr4-1024       300.00 (   0.00%)      361.00 ( -20.33%)
> Stddev    alloc-odr4-1           7.29 (   0.00%)       90.78 (-1146.00%)
> Stddev    alloc-odr4-2           3.87 (   0.00%)       51.30 (-1225.75%)
> Stddev    alloc-odr4-4           3.20 (   0.00%)       50.90 (-1491.24%)
> Stddev    alloc-odr4-8           4.67 (   0.00%)       52.23 (-1019.35%)
> Stddev    alloc-odr4-16          5.72 (   0.00%)       27.53 (-381.04%)
> Stddev    alloc-odr4-32          6.25 (   0.00%)      641.23 (-10154.46%)
> Stddev    alloc-odr4-64          2.06 (   0.00%)      386.99 (-18714.22%)
> Stddev    alloc-odr4-128        14.36 (   0.00%)       52.39 (-264.77%)
> Stddev    alloc-odr4-256        32.42 (   0.00%)      326.19 (-906.05%)
> Stddev    alloc-odr4-512        65.58 (   0.00%)      184.49 (-181.31%)
> Stddev    alloc-odr4-1024        8.88 (   0.00%)      153.01 (-1622.67%)
> Stddev    free-odr4-1            2.29 (   0.00%)      152.27 (-6549.85%)
> Stddev    free-odr4-2           10.99 (   0.00%)       73.10 (-564.89%)
> Stddev    free-odr4-4            1.99 (   0.00%)       28.40 (-1324.45%)
> Stddev    free-odr4-8            2.51 (   0.00%)       52.93 (-2007.64%)
> Stddev    free-odr4-16           2.85 (   0.00%)       26.04 (-814.88%)
> Stddev    free-odr4-32           4.04 (   0.00%)       27.05 (-569.79%)
> Stddev    free-odr4-64           2.10 (   0.00%)       48.07 (-2185.66%)
> Stddev    free-odr4-128          2.63 (   0.00%)       26.23 (-897.86%)
> Stddev    free-odr4-256          6.29 (   0.00%)       37.04 (-488.71%)
> Stddev    free-odr4-512          2.56 (   0.00%)       10.65 (-315.28%)
> Stddev    free-odr4-1024         0.95 (   0.00%)        6.46 (-582.22%)
> Max       alloc-odr4-1        8564.00 (   0.00%)     9099.00 (  -6.25%)
> Max       alloc-odr4-2        6511.00 (   0.00%)     6844.00 (  -5.11%)
> Max       alloc-odr4-4        5549.00 (   0.00%)     6038.00 (  -8.81%)
> Max       alloc-odr4-8        5045.00 (   0.00%)     5551.00 ( -10.03%)
> Max       alloc-odr4-16       4800.00 (   0.00%)     5257.00 (  -9.52%)
> Max       alloc-odr4-32       5861.00 (   0.00%)     8115.00 ( -38.46%)
> Max       alloc-odr4-64       6571.00 (   0.00%)     8292.00 ( -26.19%)
> Max       alloc-odr4-128      6930.00 (   0.00%)     8081.00 ( -16.61%)
> Max       alloc-odr4-256      7372.00 (   0.00%)     9150.00 ( -24.12%)
> Max       alloc-odr4-512     10333.00 (   0.00%)    12636.00 ( -22.29%)
> Max       alloc-odr4-1024    11035.00 (   0.00%)    12590.00 ( -14.09%)
> Max       free-odr4-1          828.00 (   0.00%)     1724.00 (-108.21%)
> Max       free-odr4-2          543.00 (   0.00%)     1192.00 (-119.52%)
> Max       free-odr4-4          354.00 (   0.00%)      519.00 ( -46.61%)
> Max       free-odr4-8          293.00 (   0.00%)      617.00 (-110.58%)
> Max       free-odr4-16         260.00 (   0.00%)      483.00 ( -85.77%)
> Max       free-odr4-32         308.00 (   0.00%)      488.00 ( -58.44%)
> Max       free-odr4-64         341.00 (   0.00%)      505.00 ( -48.09%)
> Max       free-odr4-128        346.00 (   0.00%)      497.00 ( -43.64%)
> Max       free-odr4-256        353.00 (   0.00%)      463.00 ( -31.16%)
> Max       free-odr4-512        367.00 (   0.00%)      442.00 ( -20.44%)
> Max       free-odr4-1024       303.00 (   0.00%)      381.00 ( -25.74%)
> 
> With patch test results:
>                                          patched                patched
>                                       no-monitor                monitor
> Min       alloc-odr4-1        8488.00 (   0.00%)     8514.00 (  -0.31%)
> Min       alloc-odr4-2        6551.00 (   0.00%)     6527.00 (   0.37%)
> Min       alloc-odr4-4        5536.00 (   0.00%)     5591.00 (  -0.99%)
> Min       alloc-odr4-8        5008.00 (   0.00%)     5098.00 (  -1.80%)
> Min       alloc-odr4-16       4760.00 (   0.00%)     4857.00 (  -2.04%)
> Min       alloc-odr4-32       5827.00 (   0.00%)     5919.00 (  -1.58%)
> Min       alloc-odr4-64       6561.00 (   0.00%)     6680.00 (  -1.81%)
> Min       alloc-odr4-128      6898.00 (   0.00%)     7014.00 (  -1.68%)
> Min       alloc-odr4-256      7311.00 (   0.00%)     7464.00 (  -2.09%)
> Min       alloc-odr4-512     10181.00 (   0.00%)    10286.00 (  -1.03%)
> Min       alloc-odr4-1024    11205.00 (   0.00%)    11725.00 (  -4.64%)
> Min       free-odr4-1          789.00 (   0.00%)      867.00 (  -9.89%)
> Min       free-odr4-2          490.00 (   0.00%)      526.00 (  -7.35%)
> Min       free-odr4-4          350.00 (   0.00%)      360.00 (  -2.86%)
> Min       free-odr4-8          272.00 (   0.00%)      287.00 (  -5.51%)
> Min       free-odr4-16         247.00 (   0.00%)      254.00 (  -2.83%)
> Min       free-odr4-32         298.00 (   0.00%)      304.00 (  -2.01%)
> Min       free-odr4-64         334.00 (   0.00%)      325.00 (   2.69%)
> Min       free-odr4-128        334.00 (   0.00%)      329.00 (   1.50%)
> Min       free-odr4-256        336.00 (   0.00%)      336.00 (   0.00%)
> Min       free-odr4-512        360.00 (   0.00%)      342.00 (   5.00%)
> Min       free-odr4-1024       327.00 (   0.00%)      355.00 (  -8.56%)
> Stddev    alloc-odr4-1           5.19 (   0.00%)       45.38 (-775.09%)
> Stddev    alloc-odr4-2           6.99 (   0.00%)       37.63 (-437.98%)
> Stddev    alloc-odr4-4           3.91 (   0.00%)       17.85 (-356.28%)
> Stddev    alloc-odr4-8           5.15 (   0.00%)        9.34 ( -81.47%)
> Stddev    alloc-odr4-16          3.83 (   0.00%)        5.34 ( -39.34%)
> Stddev    alloc-odr4-32          1.96 (   0.00%)       10.28 (-425.09%)
> Stddev    alloc-odr4-64          1.32 (   0.00%)      333.30 (-25141.39%)
> Stddev    alloc-odr4-128         2.06 (   0.00%)        7.37 (-258.28%)
> Stddev    alloc-odr4-256        15.56 (   0.00%)      113.48 (-629.25%)
> Stddev    alloc-odr4-512        61.25 (   0.00%)      165.09 (-169.53%)
> Stddev    alloc-odr4-1024       18.89 (   0.00%)        2.93 (  84.51%)
> Stddev    free-odr4-1            4.45 (   0.00%)       40.12 (-800.98%)
> Stddev    free-odr4-2            1.50 (   0.00%)       29.30 (-1850.31%)
> Stddev    free-odr4-4            1.27 (   0.00%)       19.49 (-1439.40%)
> Stddev    free-odr4-8            0.97 (   0.00%)        8.93 (-823.07%)
> Stddev    free-odr4-16           8.38 (   0.00%)        4.51 (  46.21%)
> Stddev    free-odr4-32           3.18 (   0.00%)        6.59 (-107.42%)
> Stddev    free-odr4-64           2.40 (   0.00%)        3.09 ( -28.50%)
> Stddev    free-odr4-128          1.55 (   0.00%)        2.53 ( -62.92%)
> Stddev    free-odr4-256          0.41 (   0.00%)        2.80 (-585.57%)
> Stddev    free-odr4-512          1.60 (   0.00%)        4.84 (-202.08%)
> Stddev    free-odr4-1024         0.66 (   0.00%)        1.19 ( -80.68%)
> Max       alloc-odr4-1        8505.00 (   0.00%)     8676.00 (  -2.01%)
> Max       alloc-odr4-2        6572.00 (   0.00%)     6651.00 (  -1.20%)
> Max       alloc-odr4-4        5552.00 (   0.00%)     5646.00 (  -1.69%)
> Max       alloc-odr4-8        5024.00 (   0.00%)     5131.00 (  -2.13%)
> Max       alloc-odr4-16       4774.00 (   0.00%)     4875.00 (  -2.12%)
> Max       alloc-odr4-32       5834.00 (   0.00%)     5950.00 (  -1.99%)
> Max       alloc-odr4-64       6565.00 (   0.00%)     7434.00 ( -13.24%)
> Max       alloc-odr4-128      6907.00 (   0.00%)     7034.00 (  -1.84%)
> Max       alloc-odr4-256      7347.00 (   0.00%)     7843.00 (  -6.75%)
> Max       alloc-odr4-512     10315.00 (   0.00%)    10866.00 (  -5.34%)
> Max       alloc-odr4-1024    11278.00 (   0.00%)    11733.00 (  -4.03%)
> Max       free-odr4-1          803.00 (   0.00%)     1009.00 ( -25.65%)
> Max       free-odr4-2          495.00 (   0.00%)      607.00 ( -22.63%)
> Max       free-odr4-4          354.00 (   0.00%)      417.00 ( -17.80%)
> Max       free-odr4-8          275.00 (   0.00%)      313.00 ( -13.82%)
> Max       free-odr4-16         273.00 (   0.00%)      272.00 (   0.37%)
> Max       free-odr4-32         309.00 (   0.00%)      324.00 (  -4.85%)
> Max       free-odr4-64         340.00 (   0.00%)      335.00 (   1.47%)
> Max       free-odr4-128        340.00 (   0.00%)      338.00 (   0.59%)
> Max       free-odr4-256        338.00 (   0.00%)      346.00 (  -2.37%)
> Max       free-odr4-512        364.00 (   0.00%)      359.00 (   1.37%)
> Max       free-odr4-1024       329.00 (   0.00%)      359.00 (  -9.12%)
> 
> The main overhead is a slight increase in latency on the memory allocation
> and free paths due to additional per-migratetype counting, with
> theoretically minimal impact on overall performance.
> 
> This patch series is based on v6.18-rc7
> 
> Hongru Zhang (3):
>   mm/page_alloc: add per-migratetype counts to buddy allocator
>   mm/vmstat: get fragmentation statistics from per-migragetype count
>   mm: optimize free_area_empty() check using per-migratetype counts
> 
>  include/linux/mmzone.h |  1 +
>  mm/internal.h          |  2 +-
>  mm/mm_init.c           |  1 +
>  mm/page_alloc.c        |  9 ++++++++-
>  mm/vmstat.c            | 30 +++++++-----------------------
>  5 files changed, 18 insertions(+), 25 deletions(-)
> 

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