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Re: [patch 4/4] Btrfs: pass __GFP_WRITE for buffered write page allocati

To: Johannes Weiner <jweiner@xxxxxxxxxx>
Subject: Re: [patch 4/4] Btrfs: pass __GFP_WRITE for buffered write page allocations
From: Josef Bacik <josef@xxxxxxxxxx>
Date: Tue, 20 Sep 2011 10:09:38 -0400
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Mel Gorman <mgorman@xxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, Wu Fengguang <fengguang.wu@xxxxxxxxx>, Jan Kara <jack@xxxxxxx>, Rik van Riel <riel@xxxxxxxxxx>, Minchan Kim <minchan.kim@xxxxxxxxx>, Chris Mason <chris.mason@xxxxxxxxxx>, "Theodore Ts'o" <tytso@xxxxxxx>, Andreas Dilger <adilger.kernel@xxxxxxxxx>, xfs@xxxxxxxxxxx, linux-btrfs@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
In-reply-to: <20110920135631.GB16338@xxxxxxxxxx>
References: <1316526315-16801-1-git-send-email-jweiner@xxxxxxxxxx> <1316526315-16801-5-git-send-email-jweiner@xxxxxxxxxx> <20110920135631.GB16338@xxxxxxxxxx>
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0.2) Gecko/20110906 Thunderbird/6.0.2
On 09/20/2011 09:56 AM, Johannes Weiner wrote:
> On Tue, Sep 20, 2011 at 03:45:15PM +0200, Johannes Weiner wrote:
>> Tell the page allocator that pages allocated for a buffered write are
>> expected to become dirty soon.
>>
>> Signed-off-by: Johannes Weiner <jweiner@xxxxxxxxxx>
>> ---
>>  fs/btrfs/file.c |    2 +-
>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
>> index e7872e4..ea1b892 100644
>> --- a/fs/btrfs/file.c
>> +++ b/fs/btrfs/file.c
>> @@ -1084,7 +1084,7 @@ static noinline int prepare_pages(struct btrfs_root 
>> *root, struct file *file,
>>  again:
>>      for (i = 0; i < num_pages; i++) {
>>              pages[i] = find_or_create_page(inode->i_mapping, index + i,
>> -                                           GFP_NOFS);
>> +                                           GFP_NOFS | __GFP_WRITE);
> 
> Btw and unrelated to this particular series, I think this should use
> grab_cache_page_write_begin() in the first place.
> 
> Most grab_cache_page calls were replaced recently (a94733d "Btrfs: use
> find_or_create_page instead of grab_cache_page") to be able to pass
> GFP_NOFS, but the pages are now also no longer __GFP_HIGHMEM and
> __GFP_MOVABLE, which irks both x86_32 and memory hotplug.
> 
> It might be better to change grab_cache_page instead to take a flags
> argument that allows passing AOP_FLAG_NOFS and revert the sites back
> to this helper?

So I can do

pages[i] = grab_cache_page_write_begin(inode->i_mapping, index + i,
                                       AOP_FLAG_NOFS);

right?  All we need is nofs, so I can just go through and change
everybody to that.  I'd rather not have to go through and change
grab_cache_page() to take a flags argument and change all the callers, I
have a bad habit of screwing stuff like that up :).  Thanks,

Josef

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