From: Haozhong Zhang <haozhong.zhang@intel.com>
To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: qemu-devel@nongnu.org, Eduardo Habkost <ehabkost@redhat.com>,
Igor Mammedov <imammedo@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
Peter Crosthwaite <crosthwaite.peter@gmail.com>,
Richard Henderson <rth@twiddle.net>,
Xiao Guangrong <guangrong.xiao@gmail.com>,
Dan Williams <dan.j.williams@intel.com>
Subject: Re: [Qemu-devel] [PATCH 2/2] hostmem-file: add an attribute 'align' to set its alignment
Date: Wed, 31 May 2017 14:24:07 +0800 [thread overview]
Message-ID: <20170531062407.ejyylcimoxkfhhrn@hz-desktop> (raw)
In-Reply-To: <20170530091624.GE11362@stefanha-x1.localdomain>
On 05/30/17 10:16 +0100, Stefan Hajnoczi wrote:
> On Fri, May 26, 2017 at 10:24:38AM +0800, Haozhong Zhang wrote:
> > file_ram_alloc() currently maps the backend file via mmap to a virtual
> > address aligned to the value returned by qemu_fd_getpagesize(). When a
> > DAX device (e.g. /dev/dax0.0) is used as the backend file, its kernel
> > mmap implementation may require an alignment larger than what
> > qemu_fd_get_pagesize() returns (e.g. 2MB vs. 4KB), and mmap may fail.
> >
> > This commit adds an attribute 'align' to hostmem-file, so that users
> > can specify a proper alignment that satisfies the kernel requirement.
> >
> > If 'align' is not specified or is 0, the value returned by
> > qemu_fd_get_pagesize() will be used as before.
>
> How are users supposed to determine alignment requirements?
As discussed in another thread [1,2], the alignment of device-dax can
be got from /sys/dev/char/$major:$minor/device/align, and I'll let
QEMU read the value from it instead of user input.
[1] https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg06235.html
[2] https://lists.gnu.org/archive/html/qemu-devel/2017-05/msg06189.html
Haozhong
next prev parent reply other threads:[~2017-05-31 6:24 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-26 2:24 [Qemu-devel] [PATCH 1/2] nvdimm: warn if the backend is not a DAX device Haozhong Zhang
2017-05-26 2:24 ` [Qemu-devel] [PATCH 2/2] hostmem-file: add an attribute 'align' to set its alignment Haozhong Zhang
2017-05-30 9:16 ` Stefan Hajnoczi
2017-05-31 6:24 ` Haozhong Zhang [this message]
2017-05-30 9:15 ` [Qemu-devel] [PATCH 1/2] nvdimm: warn if the backend is not a DAX device Stefan Hajnoczi
2017-05-31 6:12 ` Haozhong Zhang
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