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From: Matthew Wilcox <willy@infradead.org>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [PATCH 02/14] fs: Make page_mkwrite_check_truncate thp-aware
Date: Wed, 14 Oct 2020 18:23:12 +0100
Message-ID: <20201014172312.GO20115@casper.infradead.org> (raw)
In-Reply-To: <20201014161704.GF9832@magnolia>

On Wed, Oct 14, 2020 at 09:17:04AM -0700, Darrick J. Wong wrote:
> On Wed, Oct 14, 2020 at 04:03:45AM +0100, Matthew Wilcox (Oracle) wrote:
> > If the page is compound, check the last index in the page and return
> > the appropriate size.  Change the return type to ssize_t in case we ever
> > support pages larger than 2GB.
> 
> "But what about 16G pages?" :P

They're not practical with today's I/O limits; a x4 PCIe link running at
gen4 speeds will take 2 seconds to do 16GB of I/O.  Assuming doubling of PCIe
speeds every four years, and a reasonable latency of 0.1 seconds, we're
about fifteen years away from that being reasonable.  I'm sure this
code will have bitrotted by then and whoever tries to add support for
them will have work to do ...

> >  	/* page is wholly inside EOF */
> > -	if (page->index < index)
> > -		return PAGE_SIZE;
> > +	if (page->index + thp_nr_pages(page) - 1 < index)
> 
> Just curious, is this expression common enough to create a helper for
> that too?
> 
> #define thp_last_index(page) ((page)->index + thp_nr_pages(page) - 1) ?
> 
> (Maybe make that a static inline, I used a macro for brevity)

I had that in an earlier version and there were two callers, so I
took it out again because it was more effort to explain what it did
than it was to open-code it.

  reply index

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-14  3:03 [PATCH 00/14] Transparent Huge Page support for XFS Matthew Wilcox (Oracle)
2020-10-14  3:03 ` [PATCH 01/14] fs: Support THPs in vfs_dedupe_file_range Matthew Wilcox (Oracle)
2020-10-14 16:12   ` Darrick J. Wong
2020-10-14 17:16     ` Matthew Wilcox
2020-10-14  3:03 ` [PATCH 02/14] fs: Make page_mkwrite_check_truncate thp-aware Matthew Wilcox (Oracle)
2020-10-14 16:17   ` Darrick J. Wong
2020-10-14 17:23     ` Matthew Wilcox [this message]
2020-10-14  3:03 ` [PATCH 03/14] iomap: Support THPs in BIO completion path Matthew Wilcox (Oracle)
2020-10-15  9:50   ` Christoph Hellwig
2020-10-14  3:03 ` [PATCH 04/14] iomap: Support THPs in iomap_adjust_read_range Matthew Wilcox (Oracle)
2020-10-15  9:50   ` Christoph Hellwig
2020-10-14  3:03 ` [PATCH 05/14] iomap: Support THPs in invalidatepage Matthew Wilcox (Oracle)
2020-10-14 16:33   ` Darrick J. Wong
2020-10-14 17:26     ` Matthew Wilcox
2020-10-14 20:00       ` Brian Foster
2020-10-14  3:03 ` [PATCH 06/14] iomap: Support THPs in iomap_is_partially_uptodate Matthew Wilcox (Oracle)
2020-10-14  3:03 ` [PATCH 07/14] iomap: Support THPs in readpage Matthew Wilcox (Oracle)
2020-10-14 16:39   ` Darrick J. Wong
2020-10-14 17:35     ` Matthew Wilcox
2020-10-14  3:03 ` [PATCH 08/14] iomap: Support THPs in readahead Matthew Wilcox (Oracle)
2020-10-15  9:52   ` Christoph Hellwig
2020-10-14  3:03 ` [PATCH 09/14] iomap: Change iomap_write_begin calling convention Matthew Wilcox (Oracle)
2020-10-14 16:47   ` Darrick J. Wong
2020-10-14 17:41     ` Matthew Wilcox
2020-10-14 18:08       ` Matthew Wilcox
2020-10-14  3:03 ` [PATCH 10/14] iomap: Handle THPs when writing to pages Matthew Wilcox (Oracle)
2020-10-14  3:03 ` [PATCH 11/14] iomap: Support THP writeback Matthew Wilcox (Oracle)
2020-10-14  3:03 ` [PATCH 12/14] iomap: Inline data shouldn't see THPs Matthew Wilcox (Oracle)
2020-10-14  3:03 ` [PATCH 13/14] iomap: Handle tail pages in iomap_page_mkwrite Matthew Wilcox (Oracle)
2020-10-14  3:03 ` [PATCH 14/14] xfs: Support THPs Matthew Wilcox (Oracle)
2020-10-14 16:51   ` Darrick J. Wong
2020-10-14 17:30     ` Matthew Wilcox

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