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

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Message-ID: <1474940324.28155.44.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Mon, 26 Sep 2016 18:38:44 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Michal Hocko <mhocko@...nel.org>,
        netdev@...r.kernel.org
Subject: Re: [PATCH v2] fs/select: add vmalloc fallback for select(2)

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.

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