From: Eric Dumazet <eric.dumazet@gmail.com>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, Michal Hocko <mhocko@kernel.org>,
netdev@vger.kernel.org
Subject: Re: [PATCH v2] fs/select: add vmalloc fallback for select(2)
Date: Thu, 22 Sep 2016 09:49:42 -0700 [thread overview]
Message-ID: <1474562982.23058.140.camel@edumazet-glaptop3.roam.corp.google.com> (raw)
In-Reply-To: <20160922164359.9035-1-vbabka@suse.cz>
On Thu, 2016-09-22 at 18:43 +0200, Vlastimil Babka wrote:
> The select(2) syscall performs a kmalloc(size, GFP_KERNEL) where size grows
> with the number of fds passed. We had a customer report page allocation
> failures of order-4 for this allocation. This is a costly order, so it might
> easily fail, as the VM expects such allocation to have a lower-order fallback.
>
> Such trivial fallback is vmalloc(), as the memory doesn't have to be
> physically contiguous. Also the allocation is temporary for the duration of the
> syscall, so it's unlikely to stress vmalloc too much.
vmalloc() uses a vmap_area_lock spinlock, and TLB flushes.
So I guess allowing vmalloc() being called from an innocent application
doing a select() might be dangerous, especially if this select() happens
thousands of time per second.
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next prev parent reply other threads:[~2016-09-22 16:49 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-22 16:43 [PATCH v2] fs/select: add vmalloc fallback for select(2) Vlastimil Babka
2016-09-22 16:49 ` Eric Dumazet [this message]
2016-09-22 16:56 ` Vlastimil Babka
2016-09-22 17:07 ` Eric Dumazet
2016-09-22 17:55 ` Vlastimil Babka
2016-09-23 9:42 ` David Laight
2016-09-23 9:58 ` Vlastimil Babka
2016-09-23 13:35 ` David Laight
2016-09-26 10:01 ` Vlastimil Babka
2016-09-26 15:02 ` David Laight
2016-09-25 18:50 ` Andi Kleen
2016-09-27 0:01 ` Andrew Morton
2016-09-27 1:38 ` Eric Dumazet
2016-09-27 8:13 ` Vlastimil Babka
2016-09-27 13:34 ` Eric Dumazet
2016-09-27 8:06 ` Vlastimil Babka
2016-09-27 8:45 ` [PATCH v3] " Vlastimil Babka
2016-09-27 10:22 ` Michal Hocko
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