From: Matthew Wilcox <willy@infradead.org>
To: Johannes Thumshirn <Johannes.Thumshirn@wdc.com>
Cc: "linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>,
"linux-erofs@lists.ozlabs.org" <linux-erofs@lists.ozlabs.org>,
"linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>,
"linux-f2fs-devel@lists.sourceforge.net"
<linux-f2fs-devel@lists.sourceforge.net>,
"cluster-devel@redhat.com" <cluster-devel@redhat.com>,
"ocfs2-devel@oss.oracle.com" <ocfs2-devel@oss.oracle.com>,
"linux-xfs@vger.kernel.org" <linux-xfs@vger.kernel.org>
Subject: Re: [PATCH v5 01/13] mm: Fix the return type of __do_page_cache_readahead
Date: Tue, 11 Feb 2020 04:34:30 -0800 [thread overview]
Message-ID: <20200211123430.GT8731@bombadil.infradead.org> (raw)
In-Reply-To: <SN4PR0401MB3598602411B75B46F5267B829B180@SN4PR0401MB3598.namprd04.prod.outlook.com>
On Tue, Feb 11, 2020 at 08:19:14AM +0000, Johannes Thumshirn wrote:
> On 11/02/2020 02:05, Matthew Wilcox wrote:
> > even though I'm pretty sure we're not going to readahead more than 2^32
> > pages ever.
>
> And 640K is more memory than anyone will ever need on a computer *scnr*
Sure, but bandwidth just isn't increasing quickly enough to have
this make sense. 2^32 pages even on our smallest page size machines
is 16GB. Right now, we cap readahead at just 256kB. If we did try to
readahead 16GB, we'd be occupying a PCIe gen4 x4 drive for two seconds,
just satisfying this one readahead. PCIe has historically doubled in
bandwidth every three years or so, so to get this down to something
reasonable like a hundredth of a second, we're looking at PCIe gen12 in
twenty years or so. And I bet we still won't do it (also, I doubt PCIe
will continue doubling bandwidth every three years).
And Linus has forbidden individual IOs over 2GB anyway, so not happening
until he's forced to see the error of his ways ;-)
next prev parent reply other threads:[~2020-02-11 12:34 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-11 1:03 [PATCH v5 00/13] Change readahead API Matthew Wilcox
2020-02-11 1:03 ` [PATCH v5 01/13] mm: Fix the return type of __do_page_cache_readahead Matthew Wilcox
2020-02-11 8:19 ` Johannes Thumshirn
2020-02-11 12:34 ` Matthew Wilcox [this message]
2020-02-12 18:13 ` Christoph Hellwig
2020-02-14 3:19 ` John Hubbard
2020-02-14 4:21 ` Matthew Wilcox
2020-02-14 4:33 ` John Hubbard
2020-02-14 19:50 ` Matthew Wilcox
2020-02-11 1:03 ` [PATCH v5 02/13] mm: Ignore return value of ->readpages Matthew Wilcox
2020-02-12 18:13 ` Christoph Hellwig
2020-02-11 1:03 ` [PATCH v5 03/13] mm: Put readahead pages in cache earlier Matthew Wilcox
2020-02-14 3:36 ` John Hubbard
2020-02-15 1:15 ` Matthew Wilcox
2020-02-11 1:03 ` [PATCH v5 04/13] mm: Add readahead address space operation Matthew Wilcox
2020-02-11 4:52 ` Dave Chinner
2020-02-11 12:54 ` Matthew Wilcox
2020-02-11 20:08 ` Dave Chinner
2020-02-12 18:18 ` Christoph Hellwig
2020-02-14 5:36 ` John Hubbard
2020-02-15 1:15 ` Matthew Wilcox
2020-02-11 1:03 ` [PATCH v5 05/13] mm: Add page_cache_readahead_limit Matthew Wilcox
2020-02-11 1:03 ` [PATCH v5 06/13] fs: Convert mpage_readpages to mpage_readahead Matthew Wilcox
2020-02-13 22:09 ` Junxiao Bi
2020-02-11 1:03 ` [PATCH v5 07/13] btrfs: Convert from readpages to readahead Matthew Wilcox
2020-02-11 1:03 ` [PATCH v5 08/13] erofs: Convert uncompressed files " Matthew Wilcox
2020-02-11 1:03 ` [PATCH v5 09/13] erofs: Convert compressed " Matthew Wilcox
2020-02-11 1:03 ` [PATCH v5 10/13] ext4: Convert " Matthew Wilcox
2020-02-11 1:03 ` [PATCH v5 11/13] f2fs: " Matthew Wilcox
2020-02-11 1:03 ` [PATCH v5 12/13] fuse: " Matthew Wilcox
2020-02-11 1:03 ` [PATCH v5 13/13] iomap: " Matthew Wilcox
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