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In-Reply-To: <1440177121-12741-1-git-send-email-klamm@yandex-team.ru>
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	<1440177121-12741-1-git-send-email-klamm@yandex-team.ru>
Date: Fri, 21 Aug 2015 11:17:43 -0700
Message-ID: <CA+55aFyc8bb=ASmQbhk72cFOOmGpNhowdWGtSn+biog69_f+LA@mail.gmail.com>
Subject: Re: [PATCH] mm: use only per-device readahead limit
From: Linus Torvalds <torvalds@linux-foundation.org>
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To: Roman Gushchin <klamm@yandex-team.ru>
Cc: linux-mm <linux-mm@kvack.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>, Jan Kara <jack@suse.cz>, Wu Fengguang <fengguang.wu@intel.com>, David Rientjes <rientjes@google.com>, Andrew Morton <akpm@linux-foundation.org>

On Fri, Aug 21, 2015 at 10:12 AM, Roman Gushchin <klamm@yandex-team.ru> wrote:
>
> There are devices, which require custom readahead limit.
> For instance, for RAIDs it's calculated as number of devices
> multiplied by chunk size times 2.

So afaik, the default read-ahead size is 128kB, which is actually
smaller than the old 512-page limit.

Which means that you probably changed "ra_pages" somehow. Is it some
system tool that does that automatically, and if so based on what,
exactly?

I'm also slightly worried about the fact that now the max read-ahead
may actually be zero, and/or basically infinite (there's a ioctl to
set it that only tests that it's not negative). Does everything react
ok to that?

               Linus

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