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From: Brian Foster <bfoster@redhat.com>
To: Christoph Hellwig <hch@lst.de>
Cc: linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-block@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 08/34] mm: split ->readpages calls to avoid non-contiguous pages lists
Date: Tue, 22 May 2018 10:52:27 -0400	[thread overview]
Message-ID: <20180522145226.GA25251@bfoster.bfoster> (raw)
In-Reply-To: <20180518164830.1552-9-hch@lst.de>

On Fri, May 18, 2018 at 06:48:04PM +0200, Christoph Hellwig wrote:
> That way file systems don't have to go spotting for non-contiguous pages
> and work around them.  It also kicks off I/O earlier, allowing it to
> finish earlier and reduce latency.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  mm/readahead.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/readahead.c b/mm/readahead.c
> index fa4d4b767130..044ab0c137cc 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -177,8 +177,18 @@ unsigned int __do_page_cache_readahead(struct address_space *mapping,
>  		rcu_read_lock();
>  		page = radix_tree_lookup(&mapping->i_pages, page_offset);
>  		rcu_read_unlock();
> -		if (page && !radix_tree_exceptional_entry(page))
> +		if (page && !radix_tree_exceptional_entry(page)) {
> +			/*
> +			 * Page already present?  Kick off the current batch of
> +			 * contiguous pages before continuing with the next
> +			 * batch.
> +			 */
> +			if (nr_pages)
> +				read_pages(mapping, filp, &page_pool, nr_pages,
> +						gfp_mask);
> +			nr_pages = 0;
>  			continue;
> +		}

The comment at the top of this function explicitly states that we don't
submit I/Os before all of the pages are allocated. That probably needs
an update, at least.

That aside, couldn't this introduce that kind of problematic read/write
behavior if the mapping was sparsely populated for whatever reason
(every other page, for example)? Perhaps that's just too unlikely to
matter.

Brian

>  
>  		page = __page_cache_alloc(gfp_mask);
>  		if (!page)
> -- 
> 2.17.0
> 
> --
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  reply	other threads:[~2018-05-22 14:52 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-18 16:47 buffered I/O without buffer heads in xfs and iomap v2 Christoph Hellwig
2018-05-18 16:47 ` [PATCH 01/34] block: add a lower-level bio_add_page interface Christoph Hellwig
2018-05-18 16:56   ` Jens Axboe
2018-05-18 16:47 ` [PATCH 02/34] fs: factor out a __generic_write_end helper Christoph Hellwig
2018-05-18 16:47 ` [PATCH 03/34] fs: move page_cache_seek_hole_data to iomap.c Christoph Hellwig
2018-05-18 16:48 ` [PATCH 04/34] fs: remove the buffer_unwritten check in page_seek_hole_data Christoph Hellwig
2018-05-18 16:48 ` [PATCH 05/34] fs: use ->is_partially_uptodate in page_cache_seek_hole_data Christoph Hellwig
2018-05-21 19:53   ` Darrick J. Wong
2018-05-22  7:56     ` Christoph Hellwig
2018-05-18 16:48 ` [PATCH 06/34] mm: give the 'ret' variable a better name __do_page_cache_readahead Christoph Hellwig
2018-05-18 16:48 ` [PATCH 07/34] mm: return an unsigned int from __do_page_cache_readahead Christoph Hellwig
2018-05-18 16:48 ` [PATCH 08/34] mm: split ->readpages calls to avoid non-contiguous pages lists Christoph Hellwig
2018-05-22 14:52   ` Brian Foster [this message]
2018-05-18 16:48 ` [PATCH 09/34] iomap: inline data should be an iomap type, not a flag Christoph Hellwig
2018-05-18 16:48 ` [PATCH 10/34] iomap: fix the comment describing IOMAP_NOWAIT Christoph Hellwig
2018-05-18 16:48 ` [PATCH 11/34] iomap: move IOMAP_F_BOUNDARY to gfs2 Christoph Hellwig
2018-05-18 16:48 ` [PATCH 12/34] iomap: use __bio_add_page in iomap_dio_zero Christoph Hellwig
2018-05-18 16:48 ` [PATCH 13/34] iomap: add a iomap_sector helper Christoph Hellwig
2018-05-18 16:48 ` [PATCH 14/34] iomap: add an iomap-based bmap implementation Christoph Hellwig
2018-05-18 16:48 ` [PATCH 15/34] iomap: add an iomap-based readpage and readpages implementation Christoph Hellwig
2018-05-18 16:48 ` [PATCH 16/34] iomap: add initial support for writes without buffer heads Christoph Hellwig
2018-05-21 23:27   ` Darrick J. Wong
2018-05-22  0:07     ` Dave Chinner
2018-05-22  8:24       ` Christoph Hellwig
2018-05-22 22:38         ` Dave Chinner
2018-05-23  6:03           ` Christoph Hellwig
2018-05-22  8:20     ` Christoph Hellwig
2018-05-22  8:31     ` Christoph Hellwig
2018-05-22  9:39       ` Christoph Hellwig
2018-05-18 16:48 ` [PATCH 17/34] xfs: use iomap_bmap Christoph Hellwig
2018-05-18 16:48 ` [PATCH 18/34] xfs: use iomap for blocksize == PAGE_SIZE readpage and readpages Christoph Hellwig
2018-05-18 16:48 ` [PATCH 19/34] xfs: simplify xfs_bmap_punch_delalloc_range Christoph Hellwig
2018-05-18 16:48 ` [PATCH 20/34] xfs: simplify xfs_aops_discard_page Christoph Hellwig
2018-05-18 16:48 ` [PATCH 21/34] xfs: move locking into xfs_bmap_punch_delalloc_range Christoph Hellwig
2018-05-18 16:48 ` [PATCH 22/34] xfs: make xfs_writepage_map extent map centric Christoph Hellwig
2018-05-18 16:48 ` [PATCH 23/34] xfs: remove the now unused XFS_BMAPI_IGSTATE flag Christoph Hellwig
2018-05-18 16:48 ` [PATCH 24/34] xfs: remove xfs_reflink_find_cow_mapping Christoph Hellwig
2018-05-18 16:48 ` [PATCH 25/34] xfs: remove xfs_reflink_trim_irec_to_next_cow Christoph Hellwig
2018-05-18 16:48 ` [PATCH 26/34] xfs: simplify xfs_map_blocks by using xfs_iext_lookup_extent directly Christoph Hellwig
2018-05-18 16:48 ` [PATCH 27/34] xfs: don't clear imap_valid for a non-uptodate buffers Christoph Hellwig
2018-05-18 16:48 ` [PATCH 28/34] xfs: remove the imap_valid flag Christoph Hellwig
2018-05-18 16:48 ` [PATCH 29/34] xfs: don't look at buffer heads in xfs_add_to_ioend Christoph Hellwig
2018-05-18 16:48 ` [PATCH 30/34] xfs: move all writeback buffer_head manipulation into xfs_map_at_offset Christoph Hellwig
2018-05-18 16:48 ` [PATCH 31/34] xfs: remove xfs_start_page_writeback Christoph Hellwig
2018-05-18 16:48 ` [PATCH 32/34] xfs: refactor the tail of xfs_writepage_map Christoph Hellwig
2018-05-18 16:48 ` [PATCH 33/34] xfs: do not set the page uptodate in xfs_writepage_map Christoph Hellwig
2018-05-18 16:48 ` [PATCH 34/34] xfs: allow writeback on pages without buffer heads Christoph Hellwig
2018-05-21 20:46 ` buffered I/O without buffer heads in xfs and iomap v2 Darrick J. Wong
2018-05-22 20:33   ` Christoph Hellwig
2018-05-23 14:43 buffered I/O without buffer heads in xfs and iomap v3 Christoph Hellwig
2018-05-23 14:43 ` [PATCH 08/34] mm: split ->readpages calls to avoid non-contiguous pages lists Christoph Hellwig
2018-05-30  5:46   ` Darrick J. Wong

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