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This is wasteful since non-writable VMAs mapped b= y > 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 know= s > 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 mmtes= ts > benchmarks, particularly hackbench, with a maximum improvement of 12%. > > Signed-off-by: Dev Jain > --- > 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 improvem= ent, > (R) denotes statistically significant regression (Please ignore the > numbers in the middle column): > > +------------------------------------+---------------------------------= -------------------------+-----------------------+-----------------------= ---+ > | mmtests/hackbench | process-pipes-1 (seconds) = | 0.145 | -0.0= 6% | > | | process-pipes-4 (seconds) = | 0.4335 | -0.2= 7% | > | | process-pipes-7 (seconds) = | 0.823 | (I) -12.1= 3% | > | | process-pipes-12 (seconds) = | 1.3538333333333334 | (I) -5.3= 2% | > | | process-pipes-21 (seconds) = | 1.8971666666666664 | (I) -2.8= 7% | > | | process-pipes-30 (seconds) = | 2.5023333333333335 | (I) -3.3= 9% | > | | process-pipes-48 (seconds) = | 3.4305 | (I) -5.6= 5% | > | | process-pipes-79 (seconds) = | 4.245833333333334 | (I) -6.7= 4% | > | | process-pipes-110 (seconds) = | 5.114833333333333 | (I) -6.2= 6% | > | | process-pipes-141 (seconds) = | 6.1885 | (I) -4.9= 9% | > | | process-pipes-172 (seconds) = | 7.231833333333334 | (I) -4.4= 5% | > | | process-pipes-203 (seconds) = | 8.393166666666668 | (I) -3.6= 5% | > | | process-pipes-234 (seconds) = | 9.487499999999999 | (I) -3.4= 5% | > | | process-pipes-256 (seconds) = | 10.316166666666666 | (I) -3.4= 7% | > | | process-sockets-1 (seconds) = | 0.289 | 2.1= 3% | > | | process-sockets-4 (seconds) = | 0.7596666666666666 | 1.0= 2% | > | | process-sockets-7 (seconds) = | 1.1663333333333334 | -0.2= 6% | > | | process-sockets-12 (seconds) = | 1.8641666666666665 | -1.2= 4% | > | | process-sockets-21 (seconds) = | 3.0773333333333333 | 0.0= 1% | > | | process-sockets-30 (seconds) = | 4.2405 | -0.1= 5% | > | | process-sockets-48 (seconds) = | 6.459666666666666 | 0.1= 5% | > | | process-sockets-79 (seconds) = | 10.156833333333333 | 1.4= 5% | > | | process-sockets-110 (seconds) = | 14.317833333333333 | -1.6= 4% | > | | process-sockets-141 (seconds) = | 20.8735 | (I) -4.2= 7% | > | | process-sockets-172 (seconds) = | 26.205333333333332 | 0.3= 0% | > | | process-sockets-203 (seconds) = | 31.298000000000002 | -1.7= 1% | > | | process-sockets-234 (seconds) = | 36.104000000000006 | -1.9= 4% | > | | process-sockets-256 (seconds) = | 39.44016666666667 | -0.7= 1% | > | | thread-pipes-1 (seconds) = | 0.17550000000000002 | 0.6= 6% | > | | thread-pipes-4 (seconds) = | 0.44716666666666666 | 1.6= 6% | > | | thread-pipes-7 (seconds) = | 0.7345 | -0.1= 7% | > | | thread-pipes-12 (seconds) = | 1.405833333333333 | (I) -4.1= 2% | > | | thread-pipes-21 (seconds) = | 2.0113333333333334 | (I) -2.1= 3% | > | | thread-pipes-30 (seconds) = | 2.6648333333333336 | (I) -3.7= 8% | > | | thread-pipes-48 (seconds) = | 3.6341666666666668 | (I) -5.7= 7% | > | | thread-pipes-79 (seconds) = | 4.4085 | (I) -5.3= 1% | > | | thread-pipes-110 (seconds) = | 5.374666666666666 | (I) -6.1= 2% | > | | thread-pipes-141 (seconds) = | 6.385666666666666 | (I) -4.0= 0% | > | | thread-pipes-172 (seconds) = | 7.403000000000001 | (I) -3.0= 1% | > | | thread-pipes-203 (seconds) = | 8.570333333333332 | (I) -2.6= 2% | > | | thread-pipes-234 (seconds) = | 9.719166666666666 | (I) -2.0= 0% | > | | thread-pipes-256 (seconds) = | 10.552833333333334 | (I) -2.3= 0% | > | | thread-sockets-1 (seconds) = | 0.3065 | (R) 2.3= 9% | > +------------------------------------+---------------------------------= -------------------------+-----------------------+-----------------------= ---+ > > +------------------------------------+---------------------------------= -------------------------+-----------------------+-----------------------= ---+ > | mmtests/sysbench-mutex | sysbenchmutex-1 (usec) = | 194.38333333333333 | -0.0= 2% | > | | sysbenchmutex-4 (usec) = | 200.875 | -0.0= 2% | > | | sysbenchmutex-7 (usec) = | 201.23000000000002 | 0.0= 0% | > | | sysbenchmutex-12 (usec) = | 201.77666666666664 | 0.1= 2% | > | | sysbenchmutex-21 (usec) = | 203.03 | -0.4= 0% | > | | sysbenchmutex-30 (usec) = | 203.285 | 0.0= 8% | > | | sysbenchmutex-48 (usec) = | 231.30000000000004 | 2.5= 9% | > | | sysbenchmutex-79 (usec) = | 362.075 | -0.8= 0% | > | | sysbenchmutex-110 (usec) = | 516.8233333333334 | -3.8= 7% | > | | sysbenchmutex-128 (usec) = | 593.3533333333334 | (I) -4.4= 6% | > +------------------------------------+---------------------------------= -------------------------+-----------------------+-----------------------= ---+ > > mm/khugepaged.c | 9 ++------- > 1 file changed, 2 insertions(+), 7 deletions(-) > Acked-by: Zi Yan Best Regards, Yan, Zi