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5mQHinY6HajjAoVkvYPecO7TBeD8Jos6BW9GjdueKQhbpNGrchOhR21u5cOKFL2e27rINJCpZNyY0dJid2ZokyNkMT5zYPDr++QAyLoubDtflJCpNeN4qZ/FX3w9T0dcEexZ57eimR8R8thELb6XHfHDBs53z5sFtQClSq9tQUh+bJ7R0ECMd9Lm+2ikbgk/ICUYB7fO7v+Ed44S7ugvn8KqVGKFY1e7doUPWc7MusdPg5AD6YcSd5RZH4jYyHZMmo88G8s8muGTP8K4czV9uSj+MJwEgLyUPfWXbzXfmZyeuvNgCve8GJmB4VJok4epDsfUCfthmAIJzf/ZrMxwrFGyvrkaF4gjilI0Y0kzyFyKEaQzbzay03E7gRiYAuwnKl5YgkwORBTUKa1b1hGii8BR06hRdj5BgKmdDvyutGp5pJ/5b8PzrIXtQKHXU2NV54zZHIWXXts4nf4iJMGvbsGzM5FFKp3fMA3WGftNgsG/zWKz2bLHpIyB5u3Djs/Kj9dmugVNgrc8HLCLGZUwBOn3luQrYu/MSBjc8y7fWx3eOhGuY5SBmtT/L2XucI1RA8bKpfdkkY+baF0Fltlw4Bxo0AJRBHImn27ZB2LIuzEegerp9+BvsQ/pqbl18HlZjLoGT2iDprSac3MEEgFVsVxdMR67IRdFUB2n2 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 10/24/24 8:12 AM, Vlastimil Babka wrote: > Since commit efa7df3e3bb5 ("mm: align larger anonymous mappings on THP > boundaries") a mmap() of anonymous memory without a specific address > hint and of at least PMD_SIZE will be aligned to PMD so that it can > benefit from a THP backing page. > > However this change has been shown to regress some workloads > significantly. [1] reports regressions in various spec benchmarks, with > up to 600% slowdown of the cactusBSSN benchmark on some platforms. The > benchmark seems to create many mappings of 4632kB, which would have > merged to a large THP-backed area before commit efa7df3e3bb5 and now > they are fragmented to multiple areas each aligned to PMD boundary with > gaps between. The regression then seems to be caused mainly due to the > benchmark's memory access pattern suffering from TLB or cache aliasing > due to the aligned boundaries of the individual areas. > > Another known regression bisected to commit efa7df3e3bb5 is darktable > [2] [3] and early testing suggests this patch fixes the regression there > as well. > > To fix the regression but still try to benefit from THP-friendly > anonymous mapping alignment, add a condition that the size of the > mapping must be a multiple of PMD size instead of at least PMD size. In > case of many odd-sized mapping like the cactusBSSN creates, those will > stop being aligned and with gaps between, and instead naturally merge > again. Thanks for debugging this. The fix makes sense to me. Reviewed-by: Yang Shi > > Reported-by: Michael Matz > Debugged-by: Gabriel Krisman Bertazi > Closes: https://bugzilla.suse.com/show_bug.cgi?id=1229012 [1] > Reported-by: Matthias Bodenbinder > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219366 [2] > Closes: https://lore.kernel.org/all/2050f0d4-57b0-481d-bab8-05e8d48fed0c@leemhuis.info/ [3] > Fixes: efa7df3e3bb5 ("mm: align larger anonymous mappings on THP boundaries") > Cc: > Cc: Rik van Riel > Cc: Yang Shi > Signed-off-by: Vlastimil Babka > --- > mm/mmap.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 9c0fb43064b5..a5297cfb1dfc 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -900,7 +900,8 @@ __get_unmapped_area(struct file *file, unsigned long addr, unsigned long len, > > if (get_area) { > addr = get_area(file, addr, len, pgoff, flags); > - } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) { > + } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) > + && IS_ALIGNED(len, PMD_SIZE)) { > /* Ensures that larger anonymous mappings are THP aligned. */ > addr = thp_get_unmapped_area_vmflags(file, addr, len, > pgoff, flags, vm_flags);