From: Matthew Wilcox <willy@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-fsdevel@vger.kernel.org, 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 v6 08/19] mm: Add readahead address space operation
Date: Tue, 18 Feb 2020 08:10:04 -0800 [thread overview]
Message-ID: <20200218161004.GR7778@bombadil.infradead.org> (raw)
In-Reply-To: <20200218062147.GN10776@dread.disaster.area>
On Tue, Feb 18, 2020 at 05:21:47PM +1100, Dave Chinner wrote:
> On Mon, Feb 17, 2020 at 10:45:54AM -0800, Matthew Wilcox wrote:
> > From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
> >
> > This replaces ->readpages with a saner interface:
> > - Return void instead of an ignored error code.
> > - Pages are already in the page cache when ->readahead is called.
>
> Might read better as:
>
> - Page cache is already populates with locked pages when
> ->readahead is called.
Will do.
> > - Implementation looks up the pages in the page cache instead of
> > having them passed in a linked list.
>
> Add:
>
> - cleanup of unused readahead handled by ->readahead caller, not
> the method implementation.
The readpages caller does that cleanup too, so it's not an advantage
to the readahead interface.
if (mapping->a_ops->readpages) {
ret = mapping->a_ops->readpages(filp, mapping, pages, nr_pages);
/* Clean up the remaining pages */
put_pages_list(pages);
goto out;
}
> > ``readpages``
> > called by the VM to read pages associated with the address_space
> > object. This is essentially just a vector version of readpage.
> > Instead of just one page, several pages are requested.
> > readpages is only used for read-ahead, so read errors are
> > ignored. If anything goes wrong, feel free to give up.
> > + This interface is deprecated; implement readahead instead.
>
> What is the removal schedule for the deprecated interface?
I mentioned that in the cover letter; once Dave Howells has the fscache
branch merged, I'll do the remaining filesystems. Should be within the
next couple of merge windows.
> > +/* The byte offset into the file of this readahead block */
> > +static inline loff_t readahead_offset(struct readahead_control *rac)
> > +{
> > + return (loff_t)rac->_start * PAGE_SIZE;
> > +}
>
> Urk. Didn't an early page use "offset" for the page index? That
> was was "mm: Remove 'page_offset' from readahead loop" did, right?
>
> That's just going to cause confusion to have different units for
> readahead "offsets"....
We are ... not consistent anywhere in the VM/VFS with our naming.
Unfortunately.
$ grep -n offset mm/filemap.c
391: * @start: offset in bytes where the range starts
...
815: pgoff_t offset = old->index;
...
2020: unsigned long offset; /* offset into pagecache page */
...
2257: *ppos = ((loff_t)index << PAGE_SHIFT) + offset;
That last one's my favourite. Not to mention the fine distinction you
and I discussed recently between offset_in_page() and page_offset().
Best of all, even our types encode the ambiguity of an 'offset'. We have
pgoff_t and loff_t (replacing the earlier off_t).
So, new rule. 'pos' is the number of bytes into a file. 'index' is the
number of PAGE_SIZE pages into a file. We don't use the word 'offset'
at all. 'length' as a byte count and 'count' as a page count seem like
fine names to me.
> > - if (aops->readpages) {
> > + if (aops->readahead) {
> > + aops->readahead(rac);
> > + readahead_for_each(rac, page) {
> > + unlock_page(page);
> > + put_page(page);
> > + }
>
> This needs a comment to explain the unwinding that needs to be done
> here. I'm not going to remember in a year's time that this is just
> for the pages that weren't submitted by ->readahead....
ACK.
next prev parent reply other threads:[~2020-02-18 16:10 UTC|newest]
Thread overview: 111+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-17 18:45 [PATCH v6 00/19] Change readahead API Matthew Wilcox
2020-02-17 18:45 ` [PATCH v6 01/19] mm: Return void from various readahead functions Matthew Wilcox
2020-02-18 4:47 ` Dave Chinner
2020-02-18 21:05 ` John Hubbard
2020-02-18 21:21 ` Matthew Wilcox
2020-02-18 21:52 ` John Hubbard
2020-02-17 18:45 ` [PATCH v6 02/19] mm: Ignore return value of ->readpages Matthew Wilcox
2020-02-18 4:48 ` Dave Chinner
2020-02-18 21:33 ` John Hubbard
2020-02-17 18:45 ` [PATCH v6 03/19] mm: Use readahead_control to pass arguments Matthew Wilcox
2020-02-18 5:03 ` Dave Chinner
2020-02-18 13:56 ` Matthew Wilcox
2020-02-18 22:46 ` Dave Chinner
2020-02-18 22:52 ` Matthew Wilcox
2020-02-18 22:22 ` John Hubbard
2020-02-17 18:45 ` [PATCH v6 04/19] mm: Rearrange readahead loop Matthew Wilcox
2020-02-18 5:08 ` Dave Chinner
2020-02-18 13:57 ` Matthew Wilcox
2020-02-18 22:48 ` Dave Chinner
2020-02-18 22:33 ` John Hubbard
2020-02-17 18:45 ` [PATCH v6 04/16] mm: Tweak readahead loop slightly Matthew Wilcox
2020-02-18 22:57 ` John Hubbard
2020-02-18 23:00 ` John Hubbard
2020-02-17 18:45 ` [PATCH v6 05/16] mm: Put readahead pages in cache earlier Matthew Wilcox
2020-02-17 18:45 ` [PATCH v6 05/19] mm: Remove 'page_offset' from readahead loop Matthew Wilcox
2020-02-18 5:14 ` Dave Chinner
2020-02-18 23:08 ` John Hubbard
2020-02-17 18:45 ` [PATCH v6 06/16] mm: Add readahead address space operation Matthew Wilcox
2020-02-17 18:45 ` [PATCH v6 06/19] mm: rename readahead loop variable to 'i' Matthew Wilcox
2020-02-18 5:33 ` Dave Chinner
2020-02-18 23:11 ` John Hubbard
2020-02-17 18:45 ` [PATCH v6 07/16] mm: Add page_cache_readahead_limit Matthew Wilcox
2020-02-17 18:45 ` [PATCH v6 07/19] mm: Put readahead pages in cache earlier Matthew Wilcox
2020-02-18 6:14 ` Dave Chinner
2020-02-18 15:42 ` Matthew Wilcox
2020-02-19 0:59 ` Dave Chinner
2020-02-19 0:01 ` John Hubbard
2020-02-19 1:02 ` Matthew Wilcox
2020-02-19 1:13 ` John Hubbard
2020-02-19 3:24 ` John Hubbard
2020-02-19 14:41 ` Matthew Wilcox
2020-02-19 14:52 ` Christoph Hellwig
2020-02-19 15:01 ` Matthew Wilcox
2020-02-19 20:24 ` John Hubbard
2020-02-17 18:45 ` [PATCH v6 08/16] fs: Convert mpage_readpages to mpage_readahead Matthew Wilcox
2020-02-17 18:45 ` [PATCH v6 08/19] mm: Add readahead address space operation Matthew Wilcox
2020-02-18 6:21 ` Dave Chinner
2020-02-18 16:10 ` Matthew Wilcox [this message]
2020-02-19 1:04 ` Dave Chinner
2020-02-19 0:12 ` John Hubbard
2020-02-19 3:10 ` Eric Biggers
2020-02-19 3:35 ` Eric Biggers
2020-02-19 16:52 ` Matthew Wilcox
2020-02-17 18:45 ` [PATCH v6 09/16] btrfs: Convert from readpages to readahead Matthew Wilcox
2020-02-17 18:45 ` [PATCH v6 09/19] mm: Add page_cache_readahead_limit Matthew Wilcox
2020-02-18 6:31 ` Dave Chinner
2020-02-18 19:54 ` Matthew Wilcox
2020-02-19 1:08 ` Dave Chinner
2020-02-19 1:32 ` John Hubbard
2020-02-19 2:23 ` Matthew Wilcox
2020-02-19 2:46 ` John Hubbard
2020-02-17 18:45 ` [PATCH v6 10/16] erofs: Convert uncompressed files from readpages to readahead Matthew Wilcox
2020-02-17 18:45 ` [PATCH v6 10/19] fs: Convert mpage_readpages to mpage_readahead Matthew Wilcox
2020-02-18 1:51 ` [Ocfs2-devel] " Joseph Qi
2020-02-18 6:37 ` Dave Chinner
2020-02-19 2:48 ` John Hubbard
2020-02-19 3:28 ` Eric Biggers
2020-02-19 3:47 ` Matthew Wilcox
2020-02-19 3:55 ` Eric Biggers
2020-02-17 18:45 ` [PATCH v6 11/19] btrfs: Convert from readpages to readahead Matthew Wilcox
2020-02-18 6:57 ` Dave Chinner
2020-02-18 21:12 ` Matthew Wilcox
2020-02-19 1:23 ` Dave Chinner
2020-02-17 18:46 ` [PATCH v6 11/16] erofs: Convert compressed files " Matthew Wilcox
2020-02-19 2:34 ` Gao Xiang
2020-02-17 18:46 ` [PATCH v6 12/19] erofs: Convert uncompressed " Matthew Wilcox
2020-02-19 2:39 ` Gao Xiang
2020-02-19 3:04 ` Dave Chinner
2020-02-17 18:46 ` [PATCH v6 12/16] ext4: Convert " Matthew Wilcox
2020-02-17 18:46 ` [PATCH v6 13/19] erofs: Convert compressed files " Matthew Wilcox
2020-02-19 3:08 ` Dave Chinner
2020-02-17 18:46 ` [PATCH v6 13/16] f2fs: Convert " Matthew Wilcox
2020-02-17 18:46 ` [PATCH v6 14/19] ext4: " Matthew Wilcox
2020-02-19 3:16 ` Dave Chinner
2020-02-19 3:29 ` Eric Biggers
2020-02-17 18:46 ` [PATCH v6 14/16] fuse: " Matthew Wilcox
2020-02-17 18:46 ` [PATCH v6 15/19] f2fs: " Matthew Wilcox
2020-02-17 18:46 ` [PATCH v6 15/16] iomap: " Matthew Wilcox
2020-02-17 18:46 ` [PATCH v6 16/19] fuse: " Matthew Wilcox
2020-02-19 3:22 ` Dave Chinner
2020-02-17 18:46 ` [PATCH v6 16/16] mm: Use memalloc_nofs_save in readahead path Matthew Wilcox
2020-02-17 18:46 ` [PATCH v6 17/19] iomap: Restructure iomap_readpages_actor Matthew Wilcox
2020-02-19 3:17 ` John Hubbard
2020-02-19 5:35 ` Matthew Wilcox
2020-02-19 3:29 ` Dave Chinner
2020-02-19 6:04 ` Matthew Wilcox
2020-02-19 6:40 ` Dave Chinner
2020-02-19 17:06 ` Matthew Wilcox
2020-02-17 18:46 ` [PATCH v6 18/19] iomap: Convert from readpages to readahead Matthew Wilcox
2020-02-19 3:40 ` Dave Chinner
2020-02-17 18:46 ` [PATCH v6 19/19] mm: Use memalloc_nofs_save in readahead path Matthew Wilcox
2020-02-19 3:43 ` Dave Chinner
2020-02-19 5:22 ` Matthew Wilcox
2020-02-17 18:48 ` [PATCH v6 00/19] Change readahead API Matthew Wilcox
2020-02-18 4:56 ` Dave Chinner
2020-02-18 13:42 ` Matthew Wilcox
2020-02-18 21:26 ` Dave Chinner
2020-02-19 3:45 ` Dave Chinner
2020-02-19 3:48 ` Matthew Wilcox
2020-02-19 3:57 ` Dave Chinner
2020-02-18 20:49 ` John Hubbard
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