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Message-ID: <EF78EC48-5AA7-4999-99A9-181C50C35A6D@nvidia.com> Date: Wed, 03 Sep 2025 11:46:31 -0400 From: Zi Yan <ziy@...dia.com> To: Dev Jain <dev.jain@....com> Cc: akpm@...ux-foundation.org, david@...hat.com, kas@...nel.org, willy@...radead.org, hughd@...gle.com, baolin.wang@...ux.alibaba.com, lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, npache@...hat.com, ryan.roberts@....com, baohua@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/2] mm: Enable khugepaged to operate on non-writable VMAs On 3 Sep 2025, at 1:46, Dev Jain wrote: > Currently khugepaged does not collapse a region which does not have a > single writable page. This is wasteful since non-writable VMAs mapped by > the application won't benefit from THP collapse. Therefore, remove this > restriction and allow khugepaged to collapse a VMA with arbitrary > protections. > > Along with this, currently MADV_COLLAPSE does not perform a collapse on a > non-writable VMA, and this restriction is nowhere to be found on the > manpage - the restriction itself sounds wrong to me since the user knows > the protection of the memory it has mapped, so collapsing read-only > memory via madvise() should be a choice of the user which shouldn't > be overriden by the kernel. > > On an arm64 machine, an average of 5% improvement is seen on some mmtests > benchmarks, particularly hackbench, with a maximum improvement of 12%. > > Signed-off-by: Dev Jain <dev.jain@....com> > --- > RFC->v1: > Drop writable references from tracepoints > > RFC: > https://lore.kernel.org/all/20250901074817.73012-1-dev.jain@arm.com/ > > I can see performance improvements on mmtests run on an arm64 machine > comparing with 6.17-rc2. (I) denotes statistically significant improvement, > (R) denotes statistically significant regression (Please ignore the > numbers in the middle column): > > +------------------------------------+----------------------------------------------------------+-----------------------+--------------------------+ > | mmtests/hackbench | process-pipes-1 (seconds) | 0.145 | -0.06% | > | | process-pipes-4 (seconds) | 0.4335 | -0.27% | > | | process-pipes-7 (seconds) | 0.823 | (I) -12.13% | > | | process-pipes-12 (seconds) | 1.3538333333333334 | (I) -5.32% | > | | process-pipes-21 (seconds) | 1.8971666666666664 | (I) -2.87% | > | | process-pipes-30 (seconds) | 2.5023333333333335 | (I) -3.39% | > | | process-pipes-48 (seconds) | 3.4305 | (I) -5.65% | > | | process-pipes-79 (seconds) | 4.245833333333334 | (I) -6.74% | > | | process-pipes-110 (seconds) | 5.114833333333333 | (I) -6.26% | > | | process-pipes-141 (seconds) | 6.1885 | (I) -4.99% | > | | process-pipes-172 (seconds) | 7.231833333333334 | (I) -4.45% | > | | process-pipes-203 (seconds) | 8.393166666666668 | (I) -3.65% | > | | process-pipes-234 (seconds) | 9.487499999999999 | (I) -3.45% | > | | process-pipes-256 (seconds) | 10.316166666666666 | (I) -3.47% | > | | process-sockets-1 (seconds) | 0.289 | 2.13% | > | | process-sockets-4 (seconds) | 0.7596666666666666 | 1.02% | > | | process-sockets-7 (seconds) | 1.1663333333333334 | -0.26% | > | | process-sockets-12 (seconds) | 1.8641666666666665 | -1.24% | > | | process-sockets-21 (seconds) | 3.0773333333333333 | 0.01% | > | | process-sockets-30 (seconds) | 4.2405 | -0.15% | > | | process-sockets-48 (seconds) | 6.459666666666666 | 0.15% | > | | process-sockets-79 (seconds) | 10.156833333333333 | 1.45% | > | | process-sockets-110 (seconds) | 14.317833333333333 | -1.64% | > | | process-sockets-141 (seconds) | 20.8735 | (I) -4.27% | > | | process-sockets-172 (seconds) | 26.205333333333332 | 0.30% | > | | process-sockets-203 (seconds) | 31.298000000000002 | -1.71% | > | | process-sockets-234 (seconds) | 36.104000000000006 | -1.94% | > | | process-sockets-256 (seconds) | 39.44016666666667 | -0.71% | > | | thread-pipes-1 (seconds) | 0.17550000000000002 | 0.66% | > | | thread-pipes-4 (seconds) | 0.44716666666666666 | 1.66% | > | | thread-pipes-7 (seconds) | 0.7345 | -0.17% | > | | thread-pipes-12 (seconds) | 1.405833333333333 | (I) -4.12% | > | | thread-pipes-21 (seconds) | 2.0113333333333334 | (I) -2.13% | > | | thread-pipes-30 (seconds) | 2.6648333333333336 | (I) -3.78% | > | | thread-pipes-48 (seconds) | 3.6341666666666668 | (I) -5.77% | > | | thread-pipes-79 (seconds) | 4.4085 | (I) -5.31% | > | | thread-pipes-110 (seconds) | 5.374666666666666 | (I) -6.12% | > | | thread-pipes-141 (seconds) | 6.385666666666666 | (I) -4.00% | > | | thread-pipes-172 (seconds) | 7.403000000000001 | (I) -3.01% | > | | thread-pipes-203 (seconds) | 8.570333333333332 | (I) -2.62% | > | | thread-pipes-234 (seconds) | 9.719166666666666 | (I) -2.00% | > | | thread-pipes-256 (seconds) | 10.552833333333334 | (I) -2.30% | > | | thread-sockets-1 (seconds) | 0.3065 | (R) 2.39% | > +------------------------------------+----------------------------------------------------------+-----------------------+--------------------------+ > > +------------------------------------+----------------------------------------------------------+-----------------------+--------------------------+ > | mmtests/sysbench-mutex | sysbenchmutex-1 (usec) | 194.38333333333333 | -0.02% | > | | sysbenchmutex-4 (usec) | 200.875 | -0.02% | > | | sysbenchmutex-7 (usec) | 201.23000000000002 | 0.00% | > | | sysbenchmutex-12 (usec) | 201.77666666666664 | 0.12% | > | | sysbenchmutex-21 (usec) | 203.03 | -0.40% | > | | sysbenchmutex-30 (usec) | 203.285 | 0.08% | > | | sysbenchmutex-48 (usec) | 231.30000000000004 | 2.59% | > | | sysbenchmutex-79 (usec) | 362.075 | -0.80% | > | | sysbenchmutex-110 (usec) | 516.8233333333334 | -3.87% | > | | sysbenchmutex-128 (usec) | 593.3533333333334 | (I) -4.46% | > +------------------------------------+----------------------------------------------------------+-----------------------+--------------------------+ > > mm/khugepaged.c | 9 ++------- > 1 file changed, 2 insertions(+), 7 deletions(-) > Acked-by: Zi Yan <ziy@...dia.com> Best Regards, Yan, Zi
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