From: John Hubbard <jhubbard@nvidia.com>
To: Matthew Wilcox <willy@infradead.org>, <linux-fsdevel@vger.kernel.org>
Cc: <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
<linux-btrfs@vger.kernel.org>, <linux-erofs@lists.ozlabs.org>,
<linux-ext4@vger.kernel.org>,
<linux-f2fs-devel@lists.sourceforge.net>,
<cluster-devel@redhat.com>, <ocfs2-devel@oss.oracle.com>,
<linux-xfs@vger.kernel.org>
Subject: Re: [PATCH v7 11/24] mm: Move end_index check out of readahead loop
Date: Thu, 20 Feb 2020 19:50:39 -0800 [thread overview]
Message-ID: <e6ef2075-b849-299e-0f11-c6ee82b0a3c7@nvidia.com> (raw)
In-Reply-To: <20200219210103.32400-12-willy@infradead.org>
On 2/19/20 1:00 PM, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
>
> By reducing nr_to_read, we can eliminate this check from inside the loop.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
> mm/readahead.c | 15 +++++++++------
> 1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/mm/readahead.c b/mm/readahead.c
> index 07cdfbf00f4b..ace611f4bf05 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -166,8 +166,6 @@ void __do_page_cache_readahead(struct address_space *mapping,
> unsigned long lookahead_size)
> {
> struct inode *inode = mapping->host;
> - struct page *page;
> - unsigned long end_index; /* The last page we want to read */
> LIST_HEAD(page_pool);
> loff_t isize = i_size_read(inode);
> gfp_t gfp_mask = readahead_gfp_mask(mapping);
> @@ -179,22 +177,27 @@ void __do_page_cache_readahead(struct address_space *mapping,
> ._nr_pages = 0,
> };
> unsigned long i;
> + pgoff_t end_index; /* The last page we want to read */
>
> if (isize == 0)
> return;
>
> - end_index = ((isize - 1) >> PAGE_SHIFT);
> + end_index = (isize - 1) >> PAGE_SHIFT;
> + if (index > end_index)
> + return;
> + if (index + nr_to_read < index)
> + nr_to_read = ULONG_MAX - index + 1;
> + if (index + nr_to_read >= end_index)
> + nr_to_read = end_index - index + 1;
This tiny patch made me pause, because I wasn't sure at first of the exact
intent of the lines above. Once I worked it out, it seemed like it might
be helpful (or overkill??) to add a few hints for the reader, especially since
there are no hints in the function's (minimal) documentation header. What
do you think of this?
/*
* If we can't read *any* pages without going past the inodes's isize
* limit, give up entirely:
*/
if (index > end_index)
return;
/* Cap nr_to_read, in order to avoid overflowing the ULONG type: */
if (index + nr_to_read < index)
nr_to_read = ULONG_MAX - index + 1;
/* Cap nr_to_read, to avoid reading past the inode's isize limit: */
if (index + nr_to_read >= end_index)
nr_to_read = end_index - index + 1;
Either way, it looks corrected written to me, so:
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
thanks,
--
John Hubbard
NVIDIA
>
> /*
> * Preallocate as many pages as we will need.
> */
> for (i = 0; i < nr_to_read; i++) {
> - if (index + i > end_index)
> - break;
> + struct page *page = xa_load(&mapping->i_pages, index + i);
>
> BUG_ON(index + i != rac._index + rac._nr_pages);
>
> - page = xa_load(&mapping->i_pages, index + i);
> if (page && !xa_is_value(page)) {
> /*
> * Page already present? Kick off the current batch of
>
next prev parent reply other threads:[~2020-02-21 3:50 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-19 21:00 [PATCH v7 00/23] Change readahead API Matthew Wilcox
2020-02-19 21:00 ` [PATCH v7 01/24] mm: Move readahead prototypes from mm.h Matthew Wilcox
2020-02-21 2:43 ` John Hubbard
2020-02-21 21:48 ` Matthew Wilcox
2020-02-22 0:15 ` John Hubbard
2020-02-24 21:32 ` Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 02/24] mm: Return void from various readahead functions Matthew Wilcox
2020-02-24 21:33 ` Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 03/24] mm: Ignore return value of ->readpages Matthew Wilcox
2020-02-19 21:00 ` [PATCH v7 04/24] mm: Move readahead nr_pages check into read_pages Matthew Wilcox
2020-02-20 14:36 ` Zi Yan
2020-02-21 4:24 ` John Hubbard
2020-02-24 21:34 ` Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 05/24] mm: Use readahead_control to pass arguments Matthew Wilcox
2020-02-24 21:36 ` Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 06/24] mm: Rename various 'offset' parameters to 'index' Matthew Wilcox
2020-02-21 2:21 ` John Hubbard
2020-02-21 3:27 ` John Hubbard
2020-02-19 21:00 ` [PATCH v7 07/24] mm: rename readahead loop variable to 'i' Matthew Wilcox
2020-02-19 21:00 ` [PATCH v7 08/24] mm: Remove 'page_offset' from readahead loop Matthew Wilcox
2020-02-21 2:48 ` John Hubbard
2020-02-24 21:37 ` Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 09/24] mm: Put readahead pages in cache earlier Matthew Wilcox
2020-02-21 3:19 ` John Hubbard
2020-02-21 3:43 ` Matthew Wilcox
2020-02-21 4:19 ` John Hubbard
2020-02-24 21:40 ` Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 10/24] mm: Add readahead address space operation Matthew Wilcox
2020-02-20 15:00 ` Zi Yan
2020-02-20 15:10 ` Matthew Wilcox
2020-02-21 4:30 ` John Hubbard
2020-02-24 21:41 ` Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 11/24] mm: Move end_index check out of readahead loop Matthew Wilcox
2020-02-21 3:50 ` John Hubbard [this message]
2020-02-21 15:35 ` Matthew Wilcox
2020-02-21 19:41 ` John Hubbard
2020-02-19 21:00 ` [PATCH v7 12/24] mm: Add page_cache_readahead_unbounded Matthew Wilcox
2020-02-24 21:53 ` [Cluster-devel] " Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 13/24] fs: Convert mpage_readpages to mpage_readahead Matthew Wilcox
2020-02-24 21:54 ` [Cluster-devel] " Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 14/24] btrfs: Convert from readpages to readahead Matthew Wilcox
2020-02-20 9:42 ` Johannes Thumshirn
2020-02-20 13:48 ` Matthew Wilcox
2020-02-20 15:46 ` Christoph Hellwig
2020-02-20 15:54 ` Matthew Wilcox
2020-02-20 15:57 ` Christoph Hellwig
2020-02-24 21:43 ` Christoph Hellwig
2020-02-24 21:54 ` Matthew Wilcox
2020-02-24 21:57 ` Christoph Hellwig
2020-02-19 21:00 ` [PATCH v7 15/24] erofs: Convert uncompressed files " Matthew Wilcox
2020-02-19 21:00 ` [PATCH v7 16/24] erofs: Convert compressed " Matthew Wilcox
2020-02-19 21:00 ` [PATCH v7 17/24] ext4: Convert " Matthew Wilcox
2020-02-19 21:00 ` [PATCH v7 18/24] ext4: Pass the inode to ext4_mpage_readpages Matthew Wilcox
2020-02-19 21:00 ` [PATCH v7 19/24] f2fs: Convert from readpages to readahead Matthew Wilcox
2020-02-19 21:00 ` [PATCH v7 20/24] fuse: " Matthew Wilcox
2020-02-19 21:01 ` [PATCH v7 21/24] iomap: Restructure iomap_readpages_actor Matthew Wilcox
2020-02-20 15:47 ` Christoph Hellwig
2020-02-20 16:24 ` Matthew Wilcox
2020-02-24 22:17 ` Christoph Hellwig
2020-02-25 1:49 ` Matthew Wilcox
2020-02-22 0:44 ` Darrick J. Wong
2020-02-22 1:54 ` Matthew Wilcox
2020-02-23 17:55 ` Darrick J. Wong
2020-02-19 21:01 ` [PATCH v7 22/24] iomap: Convert from readpages to readahead Matthew Wilcox
2020-02-20 15:49 ` Christoph Hellwig
2020-02-20 16:57 ` Matthew Wilcox
2020-02-22 1:00 ` Darrick J. Wong
2020-02-24 4:33 ` Matthew Wilcox
2020-02-24 16:52 ` Darrick J. Wong
2020-02-22 1:03 ` Darrick J. Wong
2020-02-22 1:09 ` Matthew Wilcox
2020-02-19 21:01 ` [PATCH v7 23/24] mm: Document why we don't set PageReadahead Matthew Wilcox
2020-02-19 21:01 ` [PATCH v7 24/24] mm: Use memalloc_nofs_save in readahead path Matthew Wilcox
2020-02-20 17:54 ` [PATCH v7 00/23] Change readahead API David Sterba
2020-02-20 22:39 ` Matthew Wilcox
2020-02-21 11:59 ` David Sterba
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