linux-kernel - Re: [PATCH] [16/19] HWPOISON: Enable .remove_error

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Date:	Wed, 12 Aug 2009 18:52:14 +0900
From:	Hidehiro Kawai <hidehiro.kawai.ez@...achi.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	tytso@....edu, hch@...radead.org, mfasheh@...e.com,
	aia21@...tab.net, hugh.dickins@...cali.co.uk, swhiteho@...hat.com,
	akpm@...ux-foundation.org, npiggin@...e.de,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	fengguang.wu@...el.com,
	Satoshi OSHIMA <satoshi.oshima.fk@...achi.com>,
	Taketoshi Sakuraba <taketoshi.sakuraba.hc@...achi.com>
Subject: Re: [PATCH] [16/19] HWPOISON: Enable .remove_error_page for migration
    aware file systems

Andi Kleen wrote:

>>Generally, dropping unwritten dirty page caches is considered to be
>>risky.  So the "panic on IO error" policy has been used as usual
>>practice for some systems.  I just suggested that we adopted
>>this policy into machine check errors. 
> 
> Hmm, what we could possibly do -- as followon patches -- would be to
> let error_remove_page check the per file system panic-on-io-error
> super block setting for dirty pages and panic in this case too.  
> Unfortunately this setting is currently per file system, not generic,
> so it would need to be a fs specific check (or the flag would need
> to be moved into a generic fs superblock field first)

A generic setting would be better, so I suggested
panic_on_dirty_page_cache_corruption flag which would be checked
before invoking error_remove_page().  If we check per-filesystem
settings, we might want to notify EIO to the filesystem.
 
> I think that would be relatively clean semantics wise. Would you be 
> interested in working on patches for that? 

Yes. :-)
I will work on this as soon as I come back from summer vacation.

>>Another option is to introduce "ignore all" policy instead of
>>panicking at the beginig of memory_failure().  Perhaps it finally
>>causes SRAR machine check, and then kernel will panic or a process
>>will be killed.  Anyway, this is a topic for the next stage.
> 
> The problem is memory_failure() would then need to start distingushing
> between AR=1 and AR=0 which it doesn't today.
> 
> It could be done, but would need some more work. 

It's my understanding that memory_failure() are never called in
AR=1 case.  Is it wrong?
 
Thanks,
-- 
Hidehiro Kawai
Hitachi, Systems Development Laboratory
Linux Technology Center

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