linux-kernel - Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into highmem

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Date:	Thu, 14 Jan 2016 17:57:42 +0100
From:	Tomeu Vizoso <tomeu@...euvizoso.net>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Neil Brown <neilb@...e.com>, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2 06/11] don't put symlink bodies in pagecache into highmem

On 14 January 2016 at 17:23, Al Viro <viro@...iv.linux.org.uk> wrote:
> On Thu, Jan 14, 2016 at 04:58:48PM +0100, Tomeu Vizoso wrote:
>> > Could you add
>> >         printk(KERN_ERR "i_data = %p, i_mapping = %p, flags: %lx\n",
>> >                 &inode->i_data,
>> >                 inode->i_mapping,
>> >                 (unsigned long)inode->i_data.flags);
>> > right before the return from nfs_get_link() and see what it prints?
>>
>> Here it is:
>>
>> [  170.136956] i_data = ed9c1b04, i_mapping = ed9c1b04, flags: 24200c0
>> [  170.144567] i_data = ed9de784, i_mapping = ed9de784, flags: 24200c0
>> [  170.151457] i_data = ed9dec84, i_mapping = ed9dec84, flags: 24200c0
>> [  170.158358] i_data = ed9c3b84, i_mapping = ed9c3b84, flags: 24200c0
>> [  170.165253] i_data = ed9d4204, i_mapping = ed9d4204, flags: 24200c0
>> [  170.172131] i_data = ed9df184, i_mapping = ed9df184, flags: 24200c0
>> [  170.188804] i_data = eddbce84, i_mapping = eddbce84, flags: 24200c0
>> [  170.196158] i_data = ec904984, i_mapping = ec904984, flags: 24200c0
>> [  170.205133] i_data = ec906784, i_mapping = ec906784, flags: 24200c0
>
> Aha.  So ->i_data vs. ->i_mapping is irrelevant (as it ought to be here)
> and inode_nohighmem() should've acted on the address_space we are hitting
> here.  What do we have in flags...  ___GFP_IO | ___GFP_FS | ___GFP_HARDWALL |
> ___GFP_DIRECT_RECLAIM | ___GFP_KSWAPD_RECLAIM.  IOW, normal GFP_USER, no
> __GFP_HIGHMEM in sight.
>
> So either we have a highmem page somehow ending up in i_data before we
> set the flags, or __page_cache_alloc() done by read_cache_page() returns
> us a highmem page on GFP_USER | __GFP_COLD (or I'm misreading the things
> completely)...
>
> Could you slap
>         printk(KERN_ERR "inode: %p, pages: %ld\n",
>                 inode, inode->i_data.nrpages);
> before that read_cache_page() in nfs_get_link() and
>         printk(KERN_ERR "page_address: %p\n", page_address(page));
> right before the return?

Here it is:

[  170.715356] inode: ec8c30b0, pages: 1
[  170.719014] page_address:   (null)

https://lava.collabora.co.uk/scheduler/job/127698/log_file

Regards,

Tomeu