From: Matthew Wilcox <willy@infradead.org>
To: Miklos Szeredi <miklos@szeredi.hu>
Cc: Andrew Morton <akpm@linux-foundation.org>,
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 <linux-xfs@vger.kernel.org>,
Dave Chinner <dchinner@redhat.com>,
William Kucharski <william.kucharski@oracle.com>
Subject: Re: [PATCH v11 24/25] fuse: Convert from readpages to readahead
Date: Mon, 20 Apr 2020 04:43:00 -0700 [thread overview]
Message-ID: <20200420114300.GB5820@bombadil.infradead.org> (raw)
In-Reply-To: <CAJfpegsZF=TFQ67vABkE5ghiZoTZF+=_u8tM5U_P6jZeAmv23A@mail.gmail.com>
On Mon, Apr 20, 2020 at 01:14:17PM +0200, Miklos Szeredi wrote:
> > + for (;;) {
> > + struct fuse_io_args *ia;
> > + struct fuse_args_pages *ap;
> > +
> > + nr_pages = readahead_count(rac) - nr_pages;
>
> Hmm. I see what's going on here, but it's confusing. Why is
> __readahead_batch() decrementing the readahead count at the start,
> rather than at the end?
>
> At the very least it needs a comment about why nr_pages is calculated this way.
Because usually that's what we want. See, for example, fs/mpage.c:
while ((page = readahead_page(rac))) {
prefetchw(&page->flags);
args.page = page;
args.nr_pages = readahead_count(rac);
args.bio = do_mpage_readpage(&args);
put_page(page);
}
fuse is different because it's trying to allocate for the next batch,
not for the batch we're currently on.
I'm a little annoyed because I posted almost this exact loop here:
https://lore.kernel.org/linux-fsdevel/CAJfpegtrhGamoSqD-3Svfj3-iTdAbfD8TP44H_o+HE+g+CAnCA@mail.gmail.com/
and you said "I think that's fine", modified only by your concern
for it not being obvious that nr_pages couldn't be decremented by
__readahead_batch(), so I modified the loop slightly to assign to
nr_pages. The part you're now complaining about is unchanged.
> > + if (nr_pages > max_pages)
> > + nr_pages = max_pages;
> > + if (nr_pages == 0)
> > + break;
> > + ia = fuse_io_alloc(NULL, nr_pages);
> > + if (!ia)
> > + return;
> > + ap = &ia->ap;
> > + nr_pages = __readahead_batch(rac, ap->pages, nr_pages);
> > + for (i = 0; i < nr_pages; i++) {
> > + fuse_wait_on_page_writeback(inode,
> > + readahead_index(rac) + i);
>
> What's wrong with ap->pages[i]->index? Are we trying to wean off using ->index?
It saves reading from a cacheline? I wouldn't be surprised if the
compiler hoisted the read from rac->_index to outside the loop and just
iterated from rac->_index to rac->_index + nr_pages.
next prev parent reply other threads:[~2020-04-20 11:43 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-14 15:02 [PATCH v11 00/25] Change readahead API Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 01/25] mm: Move readahead prototypes from mm.h Matthew Wilcox
2020-04-15 9:10 ` Johannes Thumshirn
2020-04-14 15:02 ` [PATCH v11 02/25] mm: Return void from various readahead functions Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 03/25] mm: Ignore return value of ->readpages Matthew Wilcox
2020-04-15 9:17 ` Johannes Thumshirn
2020-04-14 15:02 ` [PATCH v11 04/25] mm: Move readahead nr_pages check into read_pages Matthew Wilcox
2020-04-15 9:19 ` Johannes Thumshirn
2020-04-14 15:02 ` [PATCH v11 05/25] mm: Add new readahead_control API Matthew Wilcox
2020-04-15 1:17 ` Andrew Morton
2020-04-15 2:18 ` Matthew Wilcox
2020-04-15 4:56 ` Andrew Morton
2020-04-15 11:22 ` Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 06/25] mm: Use readahead_control to pass arguments Matthew Wilcox
2020-04-15 9:30 ` Johannes Thumshirn
2020-04-14 15:02 ` [PATCH v11 07/25] mm: Rename various 'offset' parameters to 'index' Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 08/25] mm: rename readahead loop variable to 'i' Matthew Wilcox
2020-04-15 9:31 ` Johannes Thumshirn
2020-04-14 15:02 ` [PATCH v11 09/25] mm: Remove 'page_offset' from readahead loop Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 10/25] mm: Put readahead pages in cache earlier Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 11/25] mm: Add readahead address space operation Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 12/25] mm: Move end_index check out of readahead loop Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 13/25] mm: Add page_cache_readahead_unbounded Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 14/25] mm: Document why we don't set PageReadahead Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 15/25] mm: Use memalloc_nofs_save in readahead path Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 16/25] fs: Convert mpage_readpages to mpage_readahead Matthew Wilcox
2020-06-16 22:36 ` [Cluster-devel] " Andreas Gruenbacher
2020-06-17 0:32 ` Matthew Wilcox
2020-06-17 0:57 ` Andreas Grünbacher
2020-06-17 2:21 ` Matthew Wilcox
2020-06-18 12:46 ` Andreas Gruenbacher
2020-06-18 15:03 ` Matthew Wilcox
2020-06-18 16:40 ` Andreas Gruenbacher
2020-04-14 15:02 ` [PATCH v11 17/25] btrfs: Convert from readpages to readahead Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 18/25] erofs: Convert uncompressed files " Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 19/25] erofs: Convert compressed " Matthew Wilcox
2020-04-21 5:42 ` Andrew Morton
2020-04-21 7:28 ` Gao Xiang
2020-04-14 15:02 ` [PATCH v11 20/25] ext4: Convert " Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 21/25] ext4: Pass the inode to ext4_mpage_readpages Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 22/25] f2fs: Convert from readpages to readahead Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 23/25] f2fs: Pass the inode to f2fs_mpage_readpages Matthew Wilcox
2020-04-14 15:02 ` [PATCH v11 24/25] fuse: Convert from readpages to readahead Matthew Wilcox
2020-04-20 11:14 ` Miklos Szeredi
2020-04-20 11:43 ` Matthew Wilcox [this message]
2020-04-20 11:54 ` Miklos Szeredi
2020-04-14 15:02 ` [PATCH v11 25/25] iomap: " Matthew Wilcox
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