linux-kernel - Re: [PATCH] gfs2: use __vmalloc GFP

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Date:	Mon, 2 Feb 2015 01:57:23 -0500
From:	Oleg Drokin <green@...uxhacker.ru>
To:	Dave Chinner <david@...morbit.com>
Cc:	Steven Whitehouse <swhiteho@...hat.com>, cluster-devel@...hat.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm@...ck.org
Subject: Re: [PATCH] gfs2: use __vmalloc GFP_NOFS for fs-related allocations.

Hello!

On Feb 2, 2015, at 12:37 AM, Dave Chinner wrote:

> On Sun, Feb 01, 2015 at 10:59:54PM -0500, green@...uxhacker.ru wrote:
>> From: Oleg Drokin <green@...uxhacker.ru>
>> 
>> leaf_dealloc uses vzalloc as a fallback to kzalloc(GFP_NOFS), so
>> it clearly does not want any shrinker activity within the fs itself.
>> convert vzalloc into __vmalloc(GFP_NOFS|__GFP_ZERO) to better achieve
>> this goal.
>> 
>> Signed-off-by: Oleg Drokin <green@...uxhacker.ru>
>> ---
>> fs/gfs2/dir.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>> 
>> diff --git a/fs/gfs2/dir.c b/fs/gfs2/dir.c
>> index c5a34f0..6371192 100644
>> --- a/fs/gfs2/dir.c
>> +++ b/fs/gfs2/dir.c
>> @@ -1896,7 +1896,8 @@ static int leaf_dealloc(struct gfs2_inode *dip, u32 index, u32 len,
>> 
>> 	ht = kzalloc(size, GFP_NOFS | __GFP_NOWARN);
>> 	if (ht == NULL)
>> -		ht = vzalloc(size);
>> +		ht = __vmalloc(size, GFP_NOFS | __GFP_NOWARN | __GFP_ZERO,
>> +			       PAGE_KERNEL);
> That, in the end, won't help as vmalloc still uses GFP_KERNEL
> allocations deep down in the PTE allocation code. See the hacks in
> the DM and XFS code to work around this. i.e. go look for callers of
> memalloc_noio_save().  It's ugly and grotesque, but we've got no
> other way to limit reclaim context because the MM devs won't pass
> the vmalloc gfp context down the stack to the PTE allocations....

Hm, interesting.
So all the other code in the kernel that does this sort of thing (and there's quite a bit
outside of xfs and ocfs2) would not get the desired effect?

So, I did some digging in archives and found this thread from 2010 onward with various
patches and rants.
Not sure how I missed that before.

Should we have another run at this I wonder?

Bye,
    Oleg--
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