From: Stefan Hajnoczi <stefanha@gmail.com>
To: Li Zhi Hui <zhihuili@linux.vnet.ibm.com>
Cc: kwolf@redhat.com, armbru@redhat.com, qemu-devel@nongnu.org,
stefanha@linux.vnet.ibm.com
Subject: Re: [Qemu-devel] [PATCH] block: Use bdrv functions to replace file operation in qcow.c
Date: Fri, 18 Nov 2011 10:59:05 +0000 [thread overview]
Message-ID: <CAJSP0QXfetSM8zewDtrYkL9F2790UXtcS1Bh761nL5UQxE8twQ@mail.gmail.com> (raw)
In-Reply-To: <1321607573-29744-1-git-send-email-zhihuili@linux.vnet.ibm.com>
On Fri, Nov 18, 2011 at 9:12 AM, Li Zhi Hui <zhihuili@linux.vnet.ibm.com> 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;
> }
qemu-img create -f qcow test.qcow 100T
>>> 100 * 1024 * 1024 * 1024 * 1024 / ((1 << 12) * (1 << 9))
52428800
>>> 52428800 * 8
419430400
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.
Looks okay to me.
Stefan
next prev parent reply other threads:[~2011-11-18 10:59 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 [this message]
2011-11-18 11:10 ` Paolo Bonzini
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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