linux-kernel - Re: [PATCH 07/11] vfs: Unmap underlying metadata of new data buffers only when buffer is mapped

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Message-ID: <87hbydkbf2.fsf@devron.myhome.or.jp>
Date:	Thu, 18 Jun 2009 20:51:13 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Jan Kara <jack@...e.cz>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, npiggin@...e.de
Subject: Re: [PATCH 07/11] vfs: Unmap underlying metadata of new data buffers only when buffer is mapped

Jan Kara <jack@...e.cz> writes:

> When we do delayed allocation of some buffer, we want to signal to VFS that
> the buffer is new (set buffer_new) so that it properly zeros out everything.
> But we don't have the buffer mapped yet so we cannot really unmap underlying
> metadata in this state. Make VFS avoid doing unmapping of metadata when the
> buffer is not yet mapped.

I may be missing something. However, isn't the delalloc buffer ==
(buffer_mapped() | buffer_delay())? Well, anyway, if buffer is not
buffer_mapped(), e.g. truncate() works properly?

Thanks.

> diff --git a/fs/buffer.c b/fs/buffer.c
> index 80e2630..7eb1710 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -1683,8 +1683,9 @@ static int __block_write_full_page(struct inode *inode, struct page *page,
>  			if (buffer_new(bh)) {
>  				/* blockdev mappings never come here */
>  				clear_buffer_new(bh);
> -				unmap_underlying_metadata(bh->b_bdev,
> -							bh->b_blocknr);
> +				if (buffer_mapped(bh))
> +					unmap_underlying_metadata(bh->b_bdev,
> +						bh->b_blocknr);

Is this needed for writepage?

>  			}
>  		}
>  		bh = bh->b_this_page;
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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