From: Paolo Bonzini <pbonzini@redhat.com>
To: Alex Bligh <alex@alex.org.uk>, Eric Blake <eblake@redhat.com>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
"qemu-trivial@nongnu.org" <qemu-trivial@nongnu.org>,
"nbd-general@lists.sourceforge.net"
<nbd-general@lists.sourceforge.net>,
"qemu-stable@nongnu.org" <qemu-stable@nongnu.org>,
qemu block <qemu-block@nongnu.org>
Subject: Re: [Qemu-trivial] [Nbd] [Qemu-devel] [PATCH] nbd: fix trim/discard commands with a length bigger than NBD_MAX_BUFFER_SIZE
Date: Tue, 10 May 2016 19:55:56 +0200 [thread overview]
Message-ID: <573220AC.9010704@redhat.com> (raw)
In-Reply-To: <672ED845-88C6-4C96-B2DC-F4BCBD85F788@alex.org.uk>
On 10/05/2016 17:38, Alex Bligh wrote:
> > and are at the
> > mercy of however the kernel currently decides to split large requests).
>
> I am surprised TRIM doesn't get broken up the same way READ and WRITE
> do.
The payload of TRIM has constant size, so it makes sense to do that.
The kernel then self-imposes a 2GB limit in blkdev_issue_discard.
On the other hand, READ and WRITE of size n can possibly require O(n)
memory.
Paolo
WARNING: multiple messages have this Message-ID (diff)
From: Paolo Bonzini <pbonzini@redhat.com>
To: Alex Bligh <alex@alex.org.uk>, Eric Blake <eblake@redhat.com>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
"qemu-trivial@nongnu.org" <qemu-trivial@nongnu.org>,
"nbd-general@lists.sourceforge.net"
<nbd-general@lists.sourceforge.net>,
"qemu-stable@nongnu.org" <qemu-stable@nongnu.org>,
qemu block <qemu-block@nongnu.org>
Subject: Re: [Qemu-devel] [Nbd] [PATCH] nbd: fix trim/discard commands with a length bigger than NBD_MAX_BUFFER_SIZE
Date: Tue, 10 May 2016 19:55:56 +0200 [thread overview]
Message-ID: <573220AC.9010704@redhat.com> (raw)
In-Reply-To: <672ED845-88C6-4C96-B2DC-F4BCBD85F788@alex.org.uk>
On 10/05/2016 17:38, Alex Bligh wrote:
> > and are at the
> > mercy of however the kernel currently decides to split large requests).
>
> I am surprised TRIM doesn't get broken up the same way READ and WRITE
> do.
The payload of TRIM has constant size, so it makes sense to do that.
The kernel then self-imposes a 2GB limit in blkdev_issue_discard.
On the other hand, READ and WRITE of size n can possibly require O(n)
memory.
Paolo
next prev parent reply other threads:[~2016-05-10 17:56 UTC|newest]
Thread overview: 60+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-06 8:45 [Qemu-trivial] [PATCH] nbd: fix trim/discard commands with a length bigger than NBD_MAX_BUFFER_SIZE Quentin Casasnovas
2016-05-06 8:45 ` [Qemu-devel] " Quentin Casasnovas
2016-05-10 14:01 ` [Qemu-trivial] " Eric Blake
2016-05-10 14:01 ` Eric Blake
2016-05-10 15:08 ` [Qemu-trivial] [Nbd] " Alex Bligh
2016-05-10 15:08 ` [Qemu-devel] [Nbd] " Alex Bligh
2016-05-10 15:29 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Eric Blake
2016-05-10 15:29 ` [Qemu-devel] [Nbd] " Eric Blake
2016-05-10 15:38 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Alex Bligh
2016-05-10 15:38 ` [Qemu-devel] [Nbd] " Alex Bligh
2016-05-10 15:45 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Quentin Casasnovas
2016-05-10 15:45 ` [Qemu-devel] [Nbd] " Quentin Casasnovas
2016-05-10 15:49 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Alex Bligh
2016-05-10 15:49 ` [Qemu-devel] [Nbd] " Alex Bligh
2016-05-10 16:04 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Quentin Casasnovas
2016-05-10 16:04 ` [Qemu-devel] [Nbd] " Quentin Casasnovas
2016-05-10 16:23 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Alex Bligh
2016-05-10 16:23 ` [Qemu-devel] [Nbd] " Alex Bligh
2016-05-10 16:27 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Quentin Casasnovas
2016-05-10 16:27 ` [Qemu-devel] [Nbd] " Quentin Casasnovas
2016-05-11 9:38 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Paolo Bonzini
2016-05-11 9:38 ` [Qemu-devel] [Nbd] " Paolo Bonzini
2016-05-11 14:08 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Eric Blake
2016-05-11 14:08 ` [Qemu-devel] [Nbd] " Eric Blake
2016-05-11 14:55 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Alex Bligh
2016-05-11 14:55 ` [Qemu-devel] [Nbd] " Alex Bligh
2016-05-11 15:08 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Paolo Bonzini
2016-05-11 15:08 ` [Qemu-devel] [Nbd] " Paolo Bonzini
2016-05-10 17:55 ` Paolo Bonzini [this message]
2016-05-10 17:55 ` Paolo Bonzini
2016-05-11 21:12 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Wouter Verhelst
2016-05-11 21:12 ` [Qemu-devel] [Nbd] " Wouter Verhelst
2016-05-12 15:33 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Alex Bligh
2016-05-12 15:33 ` [Qemu-devel] [Nbd] " Alex Bligh
2016-05-10 15:41 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Alex Bligh
2016-05-10 15:41 ` [Qemu-devel] [Nbd] " Alex Bligh
2016-05-10 15:46 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Eric Blake
2016-05-10 15:46 ` [Qemu-devel] [Nbd] " Eric Blake
2016-05-10 15:52 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Alex Bligh
2016-05-10 15:52 ` [Qemu-devel] [Nbd] " Alex Bligh
2016-05-10 15:54 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Quentin Casasnovas
2016-05-10 15:54 ` [Qemu-devel] [Nbd] " Quentin Casasnovas
2016-05-10 16:33 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Quentin Casasnovas
2016-05-10 16:33 ` [Qemu-devel] [Nbd] " Quentin Casasnovas
2016-05-10 20:24 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Eric Blake
2016-05-10 20:24 ` [Qemu-devel] [Nbd] " Eric Blake
2016-05-10 19:13 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Michał Belczyk
2016-05-10 19:13 ` [Qemu-devel] [Nbd] " Michał Belczyk
2016-05-11 21:10 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Wouter Verhelst
2016-05-11 21:10 ` [Qemu-devel] [Nbd] " Wouter Verhelst
2016-05-11 21:06 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Wouter Verhelst
2016-05-11 21:06 ` [Qemu-devel] [Nbd] " Wouter Verhelst
2016-05-12 15:03 ` [Qemu-trivial] [Nbd] [Qemu-devel] " Alex Bligh
2016-05-12 15:03 ` [Qemu-devel] [Nbd] " Alex Bligh
2016-05-10 20:34 ` [Qemu-trivial] [Qemu-devel] " Eric Blake
2016-05-10 20:34 ` Eric Blake
2016-05-11 8:34 ` [Qemu-trivial] " Quentin Casasnovas
2016-05-11 8:34 ` Quentin Casasnovas
2016-05-11 14:11 ` [Qemu-trivial] " Eric Blake
2016-05-11 14:11 ` Eric Blake
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