From: Linus Torvalds <torvalds@linux-foundation.org>
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>
Subject: Re: [PATCH] mm: use only per-device readahead limit
Date: Fri, 21 Aug 2015 13:44:23 -0700 [thread overview]
Message-ID: <CA+55aFy8kOomnL-C5GwSpHTn+g5R7dY78C9=h-J_Rb_u=iASpg@mail.gmail.com> (raw)
In-Reply-To: <197171440188481@webcorp01e.yandex-team.ru>
On Fri, Aug 21, 2015 at 1:21 PM, Roman Gushchin <klamm@yandex-team.ru> wrote:
>
> It's just a raid driver. For instance, drivers/md/raid5.c:6898 .
Ok. That makes me a bit less nervous. I was worried there was some
admin program out there that just ups the readahead on peoples
devices, which would mean that ra_pages is some random value chosen by
crazy user space people.
> So, I like an idea to delegate the readahead limit calculation to the underlying i/o level.
Yeah, I'm not against it either. It's just that historically we've had
some issues with people over-doing readahead (because it often helps
some made-up microbenchmark), and then we end up with latency issues
when somebody does a multi-gigabyte readahead... Iirc, we had exactly
that problem with the readahead() system call at some point (long
ago).
But if it's just the default ra_pages, then that should be ok. I think
the kernel defaults are generally sane, and I hope there isn't some
crazy distro that ends up mucking with this.
Linus
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next prev parent reply other threads:[~2015-08-21 20:44 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-20 16:19 [PATCH] mm/readahead.c: fix regression caused by small " Roman Gushchin
2015-08-20 19:23 ` Linus Torvalds
2015-08-21 17:12 ` [PATCH] mm: use only per-device " Roman Gushchin
2015-08-21 18:17 ` Linus Torvalds
2015-08-21 20:21 ` Roman Gushchin
2015-08-21 20:44 ` Linus Torvalds [this message]
2015-08-24 11:57 ` [PATCH v2] " Roman Gushchin
2015-08-24 12:41 ` Konstantin Khlebnikov
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