From: Paolo Bonzini <pbonzini@redhat.com>
To: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] block: Use bdrv functions to replace file operation in qcow.c
Date: Fri, 18 Nov 2011 12:10:39 +0100 [thread overview]
Message-ID: <ja5eff$tdd$1@dough.gmane.org> (raw)
In-Reply-To: <CAJSP0QXfetSM8zewDtrYkL9F2790UXtcS1Bh761nL5UQxE8twQ@mail.gmail.com>
On 11/18/2011 11:59 AM, Stefan Hajnoczi wrote:
> + tmp = g_malloc0(sizeof(uint64_t)*l1_size);
> > + ret = bdrv_pwrite(qcow_bs, header_size, tmp, sizeof(uint64_t)*l1_size);
> > + g_free(tmp);
> > + if (ret != sizeof(uint64_t)*l1_size) {
> > + goto exit;
> > }
>
> That means 400 MB of RAM for the zero L1 table for a 100 TB image.
> Since qcow is a legacy format this probably doesn't matter in practice
> but in theory this approach can require a noticable amount of RAM.
4 MB / TB is not a big deal (you probably would like the L1 table to be
in memory all the time), but why write the L1 table at all? Since the
file was CREATed, it is already zero and you can just leave a hole in
the file.
Paolo
next prev parent reply other threads:[~2011-11-18 11:10 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-11-18 9:12 [Qemu-devel] [PATCH] block: Use bdrv functions to replace file operation in qcow.c Li Zhi Hui
2011-11-18 10:59 ` Stefan Hajnoczi
2011-11-18 11:10 ` Paolo Bonzini [this message]
2011-11-18 14:34 ` Stefan Hajnoczi
2011-11-21 10:44 ` Kevin Wolf
2011-11-21 10:53 ` Stefan Hajnoczi
2011-11-21 11:08 ` Kevin Wolf
2011-11-21 12:48 ` Paolo Bonzini
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