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

To: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Subject: Re: [patch 4/4] Btrfs: pass __GFP_WRITE for buffered write page allocations
From: Johannes Weiner <jweiner@xxxxxxxxxx>
Date: Tue, 20 Sep 2011 15:56:31 +0200
Cc: 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, Josef Bacik <josef@xxxxxxxxxx>
In-reply-to: <1316526315-16801-5-git-send-email-jweiner@xxxxxxxxxx>
References: <1316526315-16801-1-git-send-email-jweiner@xxxxxxxxxx> <1316526315-16801-5-git-send-email-jweiner@xxxxxxxxxx>
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?

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