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Re: [PATCH v2] fs/select: add vmalloc fallback for select(2)

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On 09/27/2016 03:38 AM, Eric Dumazet wrote:
> On Mon, 2016-09-26 at 17:01 -0700, Andrew Morton wrote:
>
>> I don't share Eric's concerns about performance here.  If the vmalloc()
>> is called, we're about to write to that quite large amount of memory
>> which we just allocated, and the vmalloc() overhead will be relatively
>> low.
>
> I did not care of the performance of this particular select() system
> call really, but other cpus because of more TLB invalidations.

There are many other ways to cause those, AFAIK. The reclaim/compaction
for order-3 allocation has its own impact on system, including TLB flushes.
Or a flood of mmap(MAP_POPULATE) and madvise(MADV_DONTNEED) calls...
This vmalloc() would however require raising RLIMIT_NOFILE above the defaults.

> At least CONFIG_DEBUG_PAGEALLOC=y builds should be impacted, but maybe
> we do not care.

I doubt anyone runs that in production, especially if performance is of concern.

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Re: [PATCH v2] fs/select: add vmalloc fallback for select(2) Andrew Morton <akpm@linux-foundation.org> - 2016-09-27 02:10 +0200
  Re: [PATCH v2] fs/select: add vmalloc fallback for select(2) Eric Dumazet <eric.dumazet@gmail.com> - 2016-09-27 03:40 +0200
    Re: [PATCH v2] fs/select: add vmalloc fallback for select(2) Vlastimil Babka <vbabka@suse.cz> - 2016-09-27 10:20 +0200
      Re: [PATCH v2] fs/select: add vmalloc fallback for select(2) Eric Dumazet <eric.dumazet@gmail.com> - 2016-09-27 15:40 +0200
  Re: [PATCH v2] fs/select: add vmalloc fallback for select(2) Vlastimil Babka <vbabka@suse.cz> - 2016-09-27 10:10 +0200

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