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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
Subject: Re: [PATCH v4 00/36] Large pages in the page cache
Date: Thu, 21 May 2020 17:04:11 -0700	[thread overview]
Message-ID: <20200522000411.GI28818@bombadil.infradead.org> (raw)
In-Reply-To: <20200521224906.GU2005@dread.disaster.area>

On Fri, May 22, 2020 at 08:49:06AM +1000, Dave Chinner wrote:
> Ok, so the main issue I have with the filesystem/iomap side of
> things is that it appears to be adding "transparent huge page"
> awareness to the filesysetm code, not "large page support".
> 
> For people that aren't aware of the difference between the
> transparent huge and and a normal compound page (e.g. I have no idea
> what the difference is), this is likely to cause problems,
> especially as you haven't explained at all in this description why
> transparent huge pages are being used rather than bog standard
> compound pages.

The primary reason to use a different name from compound_*
is so that it can be compiled out for systems that don't enable
CONFIG_TRANSPARENT_HUGEPAGE.  So THPs are compound pages, as they always
have been, but for a filesystem, using thp_size() will compile to either
page_size() or PAGE_SIZE depending on CONFIG_TRANSPARENT_HUGEPAGE.

Now, maybe thp_size() is the wrong name, but then you need to suggest
a better name ;-)

> And, really, why should iomap or the filesystems care if the large
> page is a THP or just a high order compound page? The interface
> for operating on these things at the page cache level should be the
> same. We already have page_size() and friends for operating on
> high order compound pages, yet the iomap stuff has this new
> thp_size() function instead of just using page_size(). THis is going
> to lead to confusion and future bugs when people who don't know the
> difference use the wrong page size function in their filesystem
> code.

There is no wrong function to use -- just one that expands to more code
in the case where CONFIG_TRANSPARENT_HUGEPAGE is disabled.

  reply	other threads:[~2020-05-22  0:04 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-15 13:16 [PATCH v4 00/36] Large pages in the page cache Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 01/36] mm: Move PageDoubleMap bit Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 02/36] mm: Simplify PageDoubleMap with PF_SECOND policy Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 03/36] mm: Allow hpages to be arbitrary order Matthew Wilcox
2020-05-28 14:19   ` Zi Yan
2020-05-15 13:16 ` [PATCH v4 04/36] mm: Introduce thp_size Matthew Wilcox
2020-05-15 13:38   ` David Hildenbrand
2020-05-15 13:16 ` [PATCH v4 05/36] mm: Introduce thp_order Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 06/36] mm: Introduce offset_in_thp Matthew Wilcox
2020-05-15 13:39   ` David Hildenbrand
2020-05-22 17:15   ` Kirill A. Shutemov
2020-05-29 12:59     ` Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 07/36] fs: Add a filesystem flag for large pages Matthew Wilcox
2020-05-21 21:55   ` Dave Chinner
2020-05-21 23:29     ` Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 08/36] fs: Do not update nr_thps for large page mappings Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 09/36] fs: Introduce i_blocks_per_page Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 10/36] fs: Make page_mkwrite_check_truncate thp-aware Matthew Wilcox
2020-05-21 22:01   ` Dave Chinner
2020-05-21 23:30     ` Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 11/36] fs: Support THPs in zero_user_segments Matthew Wilcox
2020-05-25  4:55   ` Kirill A. Shutemov
2020-05-15 13:16 ` [PATCH v4 12/36] bio: Add bio_for_each_thp_segment_all Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 13/36] iomap: Support arbitrarily many blocks per page Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 14/36] iomap: Support large pages in iomap_adjust_read_range Matthew Wilcox
2020-05-21 22:24   ` Dave Chinner
2020-05-21 23:39     ` Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 15/36] iomap: Support large pages in read paths Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 16/36] iomap: Support large pages in write paths Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 17/36] iomap: Inline data shouldn't see large pages Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 18/36] iomap: Handle tail pages in iomap_page_mkwrite Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 19/36] xfs: Support large pages Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 20/36] mm: Make prep_transhuge_page return its argument Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 21/36] mm: Add __page_cache_alloc_order Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 22/36] mm: Allow large pages to be added to the page cache Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 23/36] mm: Allow large pages to be removed from " Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 24/36] mm: Remove page fault assumption of compound page size Matthew Wilcox
2020-05-25  4:59   ` Kirill A. Shutemov
2020-05-15 13:16 ` [PATCH v4 25/36] mm: Fix total_mapcount assumption of " Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 26/36] mm: Avoid splitting large pages Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 27/36] mm: Fix truncation for pages of arbitrary size Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 28/36] mm: Support storing shadow entries for large pages Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 29/36] mm: Support retrieving tail pages from the page cache Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 30/36] mm: Support tail pages in wait_for_stable_page Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 31/36] mm: Add DEFINE_READAHEAD Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 32/36] mm: Make page_cache_readahead_unbounded take a readahead_control Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 33/36] mm: Make __do_page_cache_readahead " Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 34/36] mm: Allow PageReadahead to be set on head pages Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 35/36] mm: Add large page readahead Matthew Wilcox
2020-05-15 13:16 ` [PATCH v4 36/36] mm: Align THP mappings for non-DAX Matthew Wilcox
2020-05-26 22:05   ` William Kucharski
2020-05-26 22:20     ` Matthew Wilcox
2020-05-21 22:49 ` [PATCH v4 00/36] Large pages in the page cache Dave Chinner
2020-05-22  0:04   ` Matthew Wilcox [this message]
2020-05-22  2:57     ` Dave Chinner
2020-05-22  3:05       ` Matthew Wilcox
2020-05-25 23:07         ` Dave Chinner
2020-05-26  1:21           ` Matthew Wilcox
2020-05-28 11:00 ` William Kucharski

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