From: Kevin Wolf <kwolf@redhat.com>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>,
Alberto Garcia <berto@igalia.com>,
qemu-devel@nongnu.org, qemu-block@nongnu.org
Subject: Re: [Qemu-devel] [Qemu-block] [PATCH] qcow2: do lazy allocation of the L2 cache
Date: Fri, 24 Apr 2015 11:52:14 +0200 [thread overview]
Message-ID: <20150424095214.GB3838@noname.redhat.com> (raw)
In-Reply-To: <20150424092621.GD13278@stefanha-thinkpad.redhat.com>
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Am 24.04.2015 um 11:26 hat Stefan Hajnoczi geschrieben:
> The posix_memalign() call wastes memory. I compared:
>
> posix_memalign(&memptr, 65536, 2560 * 65536);
> memset(memptr, 0, 2560 * 65536);
>
> with:
>
> for (i = 0; i < 2560; i++) {
> posix_memalign(&memptr, 65536, 65536);
> memset(memptr, 0, 65536);
> }
64k alignment is too much, in practice you need 512b or 4k, which
probably wastes a lot less memory.
But I just looked at the qcow2 cache code and you're right anyway.
Allocating one big block instead of many small allocations in a loop
looks like a good idea either way.
Kevin
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next prev parent reply other threads:[~2015-04-24 9:53 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-21 15:20 [Qemu-devel] [PATCH] qcow2: do lazy allocation of the L2 cache Alberto Garcia
2015-04-22 10:26 ` [Qemu-devel] [Qemu-block] " Stefan Hajnoczi
2015-04-22 14:37 ` Alberto Garcia
2015-04-23 10:15 ` Stefan Hajnoczi
2015-04-23 11:50 ` Alberto Garcia
2015-04-24 9:26 ` Stefan Hajnoczi
2015-04-24 9:45 ` Kevin Wolf
2015-04-24 9:52 ` Kevin Wolf [this message]
2015-04-24 11:10 ` Alberto Garcia
2015-04-24 12:37 ` Stefan Hajnoczi
2015-04-24 12:50 ` Alberto Garcia
2015-04-24 13:04 ` Kevin Wolf
2015-05-08 9:00 ` Alberto Garcia
2015-05-08 9:47 ` Kevin Wolf
2015-05-08 11:47 ` Alberto Garcia
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