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From: Christoph Hellwig <hch@infradead.org>
To: Jan Kara <jack@suse.cz>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	"Theodore Ts'o" <tytso@mit.edu>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	Jan Kara <jack@suse.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Hugh Dickins <hughd@google.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Matthew Wilcox <willy@infradead.org>,
	Ross Zwisler <ross.zwisler@linux.intel.com>,
	linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	linux-block@vger.kernel.org
Subject: Re: [PATCHv3 15/41] filemap: handle huge pages in do_generic_file_read()
Date: Wed, 2 Nov 2016 07:36:12 -0700	[thread overview]
Message-ID: <20161102143612.GA4790@infradead.org> (raw)
In-Reply-To: <20161101163940.GA5459@quack2.suse.cz>

On Tue, Nov 01, 2016 at 05:39:40PM +0100, Jan Kara wrote:
> I'd also note that having PMD-sized pages has some obvious disadvantages as
> well:
> 
> 1) I'm not sure buffer head handling code will quite scale to 512 or even
> 2048 buffer_heads on a linked list referenced from a page. It may work but
> I suspect the performance will suck. 

buffer_head handling always sucks.  For the iomap based bufferd write
path I plan to support a buffer_head-less mode for the block size ==
PAGE_SIZE case in 4.11 latest, but if I get enough other things of my
plate in time even for 4.10.  I think that's the right way to go for
THP, especially if we require the fs to allocate the whole huge page
as a single extent, similar to the DAX PMD mapping case.

> 2) PMD-sized pages result in increased space & memory usage.

How so?

> 3) In ext4 we have to estimate how much metadata we may need to modify when
> allocating blocks underlying a page in the worst case (you don't seem to
> update this estimate in your patch set). With 2048 blocks underlying a page,
> each possibly in a different block group, it is a lot of metadata forcing
> us to reserve a large transaction (not sure if you'll be able to even
> reserve such large transaction with the default journal size), which again
> makes things slower.

As said above I think we should only use huge page mappings if there is
a single underlying extent, same as in DAX to keep the complexity down.

> 4) As you have noted some places like write_begin() still depend on 4k
> pages which creates a strange mix of places that use subpages and that use
> head pages.

Just use the iomap bufferd I/O code and all these issues will go away.

  parent reply	other threads:[~2016-11-02 14:36 UTC|newest]

Thread overview: 75+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-15 11:54 [PATCHv3 00/41] ext4: support of huge pages Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 01/41] tools: Add WARN_ON_ONCE Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 02/41] radix tree test suite: Allow GFP_ATOMIC allocations to fail Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 03/41] radix-tree: Add radix_tree_join Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 04/41] radix-tree: Add radix_tree_split Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 05/41] radix-tree: Add radix_tree_split_preload() Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 06/41] radix-tree: Handle multiorder entries being deleted by replace_clear_tags Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 07/41] mm, shmem: swich huge tmpfs to multi-order radix-tree entries Kirill A. Shutemov
2016-09-16 12:07   ` Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 08/41] Revert "radix-tree: implement radix_tree_maybe_preload_order()" Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 09/41] page-flags: relax page flag policy for few flags Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 10/41] mm, rmap: account file thp pages Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 11/41] thp: try to free page's buffers before attempt split Kirill A. Shutemov
2016-10-11 15:40   ` Jan Kara
2016-10-11 21:43     ` Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 12/41] thp: handle write-protection faults for file THP Kirill A. Shutemov
2016-10-11 15:47   ` Jan Kara
2016-10-11 21:47     ` Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 13/41] truncate: make sure invalidate_mapping_pages() can discard huge pages Kirill A. Shutemov
2016-10-11 15:58   ` Jan Kara
2016-10-11 21:53     ` Kirill A. Shutemov
2016-10-12  6:43       ` Jan Kara
2016-10-24 10:41         ` Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 14/41] filemap: allocate huge page in page_cache_read(), if allowed Kirill A. Shutemov
2016-10-11 16:15   ` Jan Kara
2016-10-11 21:57     ` Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 15/41] filemap: handle huge pages in do_generic_file_read() Kirill A. Shutemov
2016-10-13  9:33   ` Jan Kara
2016-10-31 18:10     ` Kirill A. Shutemov
2016-11-01 16:39       ` Jan Kara
2016-11-02  8:32         ` Kirill A. Shutemov
2016-11-02 14:37           ` Christoph Hellwig
2016-11-03 20:40           ` Jan Kara
2016-11-07 11:07             ` Kirill A. Shutemov
2016-11-07 14:59               ` Christoph Hellwig
2016-11-02 14:36         ` Christoph Hellwig [this message]
2016-11-03 17:56           ` Jan Kara
2016-11-07 11:13           ` Kirill A. Shutemov
2016-11-07 15:01             ` Christoph Hellwig
2016-11-07 16:03               ` Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 16/41] filemap: allocate huge page in pagecache_get_page(), if allowed Kirill A. Shutemov
2016-09-15 11:54 ` [PATCHv3 17/41] filemap: handle huge pages in filemap_fdatawait_range() Kirill A. Shutemov
2016-10-13  9:44   ` Jan Kara
2016-10-13 12:08     ` Kirill A. Shutemov
2016-10-13 13:18       ` Jan Kara
2016-10-24 11:36         ` Kirill A. Shutemov
2016-10-30 17:31           ` Jan Kara
2016-09-15 11:55 ` [PATCHv3 18/41] HACK: readahead: alloc huge pages, if allowed Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 19/41] block: define BIO_MAX_PAGES to HPAGE_PMD_NR if huge page cache enabled Kirill A. Shutemov
2016-09-16 12:09   ` Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 20/41] mm: make write_cache_pages() work on huge pages Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 21/41] thp: introduce hpage_size() and hpage_mask() Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 22/41] thp: do not threat slab pages as huge in hpage_{nr_pages,size,mask} Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 23/41] fs: make block_read_full_page() be able to read huge page Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 24/41] fs: make block_write_{begin,end}() be able to handle huge pages Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 25/41] fs: make block_page_mkwrite() aware about " Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 26/41] truncate: make truncate_inode_pages_range() " Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 27/41] truncate: make invalidate_inode_pages2_range() " Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 28/41] mm, hugetlb: switch hugetlbfs to multi-order radix-tree entries Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 29/41] ext4: make ext4_mpage_readpages() hugepage-aware Kirill A. Shutemov
2016-09-15 12:27   ` Andreas Dilger
2016-09-16 12:17     ` Kirill A. Shutemov
2016-09-16 12:10   ` Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 30/41] ext4: make ext4_writepage() work on huge pages Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 31/41] ext4: handle huge pages in ext4_page_mkwrite() Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 32/41] ext4: handle huge pages in __ext4_block_zero_page_range() Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 33/41] ext4: make ext4_block_write_begin() aware about huge pages Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 34/41] ext4: handle huge pages in ext4_da_write_end() Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 35/41] ext4: make ext4_da_page_release_reservation() aware about huge pages Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 36/41] ext4: handle writeback with " Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 37/41] ext4: make EXT4_IOC_MOVE_EXT work " Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 38/41] ext4: fix SEEK_DATA/SEEK_HOLE for " Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 39/41] ext4: make fallocate() operations work with " Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 40/41] mm, fs, ext4: expand use of page_mapping() and page_to_pgoff() Kirill A. Shutemov
2016-09-15 11:55 ` [PATCHv3 41/41] ext4, vfs: add huge= mount option Kirill A. Shutemov

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