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This > only occurs for file folios smaller than PMD_SIZE. > > The comment suggests that this approach prevents RSS inflation. > However, it only prevents RSS accounting. The folio is still mapped to > the process, and the fact that it is mapped by a single PTE does not > affect memory pressure. Additionally, the kernel's ability to map > large folios as PMD if they are large enough does not support this > argument. > > When possible, map large folios in one shot. This reduces the number of > minor page faults and allows for TLB coalescing. > > Mapping large folios at once will allow the rmap code to mlock it on > add, as it will recognize that it is fully mapped and mlocking is safe. > We run will-it-scale micro-benchmark as part of our weekly CI for Kernel Performance Regression testing between a stable vs rc kernel. We were able to observe drastic performance gain on AMD platforms (Turin and Bergamo) with running the will-it-scale-process-page-fault3 variant between the kernels v6.17 and v6.18-rc1 in the range of 322-400%. Bisecting further landed me onto this commit (19773df031bcc67d5caa06bf0ddbbff40174be7a) as the first commit to cause this gain. The following were the machines' configuration and test parameters used:- Model name: AMD EPYC 128-Core Processor [Bergamo] Thread(s) per core: 2 Core(s) per socket: 128 Socket(s): 1 Total online memory: 258G Model name: AMD EPYC 64-Core Processor [Turin] Thread(s) per core: 2 Core(s) per socket: 64 Socket(s): 1 Total online memory: 258G Test params: nr_task: [1 8 64 128 192 256] mode: process test: page_fault3 kpi: per_process_ops cpufreq_governor: performance The following are the stats after bisection:- KPI v6.17 %diff v6.16-rc1 %diff v6.17-with19773df031 ----- ------ ----- --------- ----- -------------------- per_ process_ 936152 +322 3954402 +339 4109353 ops I have even checked the numbers built with the patch set[1] which was a fix to the regression reported[2], to see if the gain holds good and yes indeed it is. per_process_ops %diff (w.r.t baseline v6.17) --------------- ---------------------------- v6.17.0-withfixpatch: 3968637 +324 [1] http://lore.kernel.org/all/20251020163054.1063646-1-kirill@shutemov.name/ [2] https://lore.kernel.org/all/20251014175214.GW6188@frogsfrogsfrogs/ Recreation steps: 1) git clone https://github.com/antonblanchard/will-it-scale.git 2) git clone https://github.com/intel/lkp-tests.git 3) cd will-it-scale && git apply lkp-tests/programs/will-it-scale/pkg/will-it-scale.patch 4) make 5) python3 runtest.py page_fault3 25 process 0 0 1 8 64 128 192 256 NOTE: [5] is specific to machine's architecture. starting from 1 is the array of no.of tasks that you'd wish to run the testcase which here is no.cores per CCX, per NUMA node/ per Socket, nr_threads. > Signed-off-by: Kiryl Shutsemau > Reviewed-by: Shakeel Butt > Reviewed-by: Baolin Wang > --- > mm/memory.c | 9 ++------- > 1 file changed, 2 insertions(+), 7 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 0ba4f6b71847..812a7d9f6531 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -5386,13 +5386,8 @@ vm_fault_t finish_fault(struct vm_fault *vmf) > > nr_pages = folio_nr_pages(folio); > > - /* > - * Using per-page fault to maintain the uffd semantics, and same > - * approach also applies to non shmem/tmpfs faults to avoid > - * inflating the RSS of the process. > - */ > - if (!vma_is_shmem(vma) || unlikely(userfaultfd_armed(vma)) || > - unlikely(needs_fallback)) { > + /* Using per-page fault to maintain the uffd semantics */ > + if (unlikely(userfaultfd_armed(vma)) || unlikely(needs_fallback)) { > nr_pages = 1; > } else if (nr_pages > 1) { > pgoff_t idx = folio_page_idx(folio, page); Thanks and Regards, Suneeth D