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[Xen-devel] Re: [RFC PATCH 33/33] Add Xen virtual block device driver.

To: Arjan van de Ven <arjan@xxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [RFC PATCH 33/33] Add Xen virtual block device driver.
From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Date: Tue, 18 Jul 2006 13:57:18 -0700
Cc: Andrew Morton <akpm@xxxxxxxx>, Zachary Amsden <zach@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Ian Pratt <ian.pratt@xxxxxxxxxxxxx>, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, Andi Kleen <ak@xxxxxxx>, Chris Wright <chrisw@xxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, Christian Limpach <Christian.Limpach@xxxxxxxxxxxx>
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Arjan van de Ven wrote:
as first general comment, I think that some of the memory allocation
GFP_ flags are possibly incorrect; I would expect several places to use
GFP_NOIO rather than GFP_KERNEL, to avoid recursion/deadlocks

+static void blkif_recover(struct blkfront_info *info)

+       /* Stage 1: Make a safe copy of the shadow state. */
+       copy = kmalloc(sizeof(info->shadow), GFP_KERNEL | __GFP_NOFAIL);

like here..

and __GFP_NOFAIL is usually horrid; is this because error recovery was
an afterthought, or because it's physically impossible? In addition
__GFP_NOFAIL in a block device driver is... an interesting way to add
OOM deadlocks... have the VM guys looked into this yet?

In this particular case, it's only used on the resume path, which I'm guessing would not lead to IO recursion. There doesn't seem to be any particular reason for this to be NOFAIL though (but I haven't really analyzed it).

There don't appear to be any memory allocations on the IO path; they're all in setup code.


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