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[Xen-users] O_DIRECT for file-backed dom-U devices?

  • To: xen-users <xen-users@xxxxxxxxxxxxxxxxxxx>
  • From: Roland Paterson-Jones <roland@xxxxxxxxxxxx>
  • Date: Wed, 11 May 2005 17:28:01 +0200
  • Delivery-date: Wed, 11 May 2005 16:00:55 +0000
  • List-id: Xen user discussion <xen-users.lists.xensource.com>

Hi again

It struck me that dom-U and dom-0 might be inadvertantly caching the same data.

For example, if a dom-U device is backed by a dom-0 device, is there anything specifically stopping dom-0 from caching the underlying block device (I presume theres some block-device-level caching?).

Even worse, with dom-U device backed by a loop-back file, it seems that the same data could be cached in dom-U at the file level and block level, and then again in dom-0 (for the FS containing the loop-back file) at the file and block level.

Are loop-back files specifically opened with O_DIRECT or similar when mounted as loop-back to prevent this?

Or maybe I'm just confused.

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