On 10/27/20 11:35 AM, Jann Horn wrote: > On Tue, Oct 27, 2020 at 8:05 AM Michael Kerrisk (man-pages) > <mtk.manpages@xxxxxxxxx> wrote: >> On 10/12/20 4:52 PM, Jann Horn wrote: >>> On Mon, Oct 12, 2020 at 1:49 PM Jann Horn <jannh@xxxxxxxxxx> wrote: >>>> Since 34e55232e59f7b19050267a05ff1226e5cd122a5 (introduced back in >>>> v2.6.34), Linux uses per-thread RSS counters to reduce cache contention on >>>> the per-mm counters. With a 4K page size, that means that you can end up >>>> with the counters off by up to 252KiB per thread. >>> >>> Actually, as Mark Mossberg pointed out to me off-thread, the counters >>> can actually be off by many times more... >> >> So, does your patch to proc.5 need tweaking, or can I just apply as is? > > The "(up to 63 pages per thread)" would have to go, the rest should be correct. > > But as Michal said, if someone volunteers to get rid of this > optimization, maybe we don't need the documentation after all? But > that would probably require actually doing some careful > heavily-multithreaded benchmarking on a big machine with a few dozen > cores, or something like that, so that we know whether this > optimization actually is unimportant enough that we can just get rid > of it... Okay -- in the meantime, I've applied your patch, with your suggested edit, to remove "(up to 63 pages per thread)". Thanks! Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
