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AclAAqwasSHckLuuy6Lh+Z0sdiyfN80np7ylbxwQP9lwYStqZOgAREA/PjiKYzS3RzER6fk8vyUDKp2sCLLzJdZthsZSMF44rFsucb/cJYt8F2rNvmpSbFvK9FfdfxcoLtY3jinm6730xu5BDgeHvPdRgpuooSmQfwNL6xSpCSo2DVjj/s8ewsnB77/XS0zOK/y53m16NMc5Yg1wXZa6miYQJFuk2VjVH3J0PcOI049OAH3PYKlFGVqZbnof5C7JLCxkNhh8ZSlzb9zPX/xQgG/6/JEF3SHM5E7sL8HuKYPXORy5Y5RvZoupK3Yn9ZtSzX/6l/RJ5omLK8MdBFI2xMH1bLwuTjA6gVmhc1UeQGQvFdDV8DByJ2vA4nZ0Y3MUACSfSXrw7Wt85fxlHCFMzd7mxgEMwLUBfareHKxuj8fvKG00= 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 12/22/2023 2:14 AM, Matthew Wilcox wrote: > On Thu, Dec 21, 2023 at 10:07:09AM -0800, Yang Shi wrote: >> On Wed, Dec 20, 2023 at 8:49 PM Matthew Wilcox wrote: >>> >>> On Thu, Dec 21, 2023 at 08:58:42AM +0800, Yin Fengwei wrote: >>>> Yes. MAP_STACK is also mentioned in manpage of mmap. I did test to >>>> filter out of the MAP_STACK mapping based on this patch. The regression >>>> in stress-ng.pthread was gone. I suppose this is kind of safe because >>>> the madvise call is only applied to glibc allocated stack. >>>> >>>> >>>> But what I am not sure was whether it's worthy to do such kind of change >>>> as the regression only is seen obviously in micro-benchmark. No evidence >>>> showed the other regressionsin this report is related with madvise. At >>>> least from the perf statstics. Need to check more on stream/ramspeed. >>> >>> FWIW, we had a customer report a significant performance problem when >>> inadvertently using 2MB pages for stacks. They were able to avoid it by >>> using 2044KiB sized stacks ... >> >> Thanks for the report. This provided more justification regarding >> honoring MAP_STACK on Linux. Some applications, for example, pthread, >> just allocate a fixed size area for stack. This confuses kernel >> because kernel tell stack by VM_GROWSDOWN | VM_GROWSUP. >> >> But I'm still a little confused by why THP for stack could result in >> significant performance problems. Unless the applications resize the >> stack quite often. > > We didn't delve into what was causing the problem, only that it was > happening. The application had many threads, so it could have been as > simple as consuming all the available THP and leaving fewer available > for other uses. Or it could have been a memory consumption problem; > maybe the app would only have been using 16-32kB per thread but was > now using 2MB per thread and if there were, say, 100 threads, that's an > extra 199MB of memory in use. One thing I know is related with the memory zeroing. This is from the perf data in this report: 0.00 +16.7 16.69 ± 7% perf-profile.calltrace.cycles-pp.clear_page_erms.clear_huge_page.__do_huge_pmd_anonymous_page.__handle_mm_fault.handle_mm_fault Zeroing 2M memory costs much more CPU than zeroing 16-32KB memory if there are many threads. Regards Yin, Fengwei