linux-kernel - Re: [PATCH] squashfs: enable __GFP_FS in ->readpage to prevent hang in mem alloc

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Message-ID: <20181217093337.GC30879@dhcp22.suse.cz>
Date:   Mon, 17 Dec 2018 10:33:37 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Hou Tao <houtao1@...wei.com>, phillip@...ashfs.org.uk,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH] squashfs: enable __GFP_FS in ->readpage to prevent hang
 in mem alloc

On Sun 16-12-18 19:51:57, Matthew Wilcox wrote:
[...]
> Ah, yes, that makes perfect sense.  Thank you for the explanation.
> 
> I wonder if the correct fix, however, is not to move the check for
> GFP_NOFS in out_of_memory() down to below the check whether to kill
> the current task.  That would solve your problem, and I don't _think_
> it would cause any new ones.  Michal, you touched this code last, what
> do you think?

What do you mean exactly? Whether we kill a current task or something
else doesn't change much on the fact that NOFS is a reclaim restricted
context and we might kill too early. If the fs can do GFP_FS then it is
obviously a better thing to do because FS metadata can be reclaimed as
well and therefore there is potentially less memory pressure on
application data.
-- 
Michal Hocko
SUSE Labs