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[PATCHv6 11/37] HACK: readahead: alloc huge pages, if allowed

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Most page cache allocation happens via readahead (sync or async), so if
we want to have significant number of huge pages in page cache we need
to find a ways to allocate them from readahead.

Unfortunately, huge pages doesn't fit into current readahead design:
128 max readahead window, assumption on page size, PageReadahead() to
track hit/miss.

I haven't found a ways to get it right yet.

This patch just allocates huge page if allowed, but doesn't really
provide any readahead if huge page is allocated. We read out 2M a time
and I would expect spikes in latancy without readahead.

Therefore HACK.

Having that said, I don't think it should prevent huge page support to
be applied. Future will show if lacking readahead is a big deal with
huge pages in page cache.

Any suggestions are welcome.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 mm/readahead.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index c4ca70239233..289527a06254 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -174,6 +174,21 @@ int __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
 		if (page_offset > end_index)
 			break;
 
+		if (IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE) &&
+				(!page_idx || !(page_offset % HPAGE_PMD_NR)) &&
+				page_cache_allow_huge(mapping, page_offset)) {
+			page = __page_cache_alloc_order(gfp_mask | __GFP_COMP,
+					HPAGE_PMD_ORDER);
+			if (page) {
+				prep_transhuge_page(page);
+				page->index = round_down(page_offset,
+						HPAGE_PMD_NR);
+				list_add(&page->lru, &page_pool);
+				ret++;
+				goto start_io;
+			}
+		}
+
 		rcu_read_lock();
 		page = radix_tree_lookup(&mapping->page_tree, page_offset);
 		rcu_read_unlock();
@@ -189,7 +204,7 @@ int __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
 			SetPageReadahead(page);
 		ret++;
 	}
-
+start_io:
 	/*
 	 * Now start the IO.  We ignore I/O errors - if the page is not
 	 * uptodate then the caller will launch readpage again, and
-- 
2.11.0

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[PATCHv6 00/37] ext4: support of huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:00 +0100
  [PATCHv6 03/37] page-flags: relax page flag policy for few flags "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:00 +0100
  [PATCHv6 36/37] mm, fs, ext4: expand use of page_mapping() and page_to_pgoff() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:00 +0100
  [PATCHv6 06/37] thp: handle write-protection faults for file THP "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:00 +0100
    Re: [PATCHv6 06/37] thp: handle write-protection faults for file THP Matthew Wilcox <willy@infradead.org> - 2017-01-26 16:50 +0100
      Re: [PATCHv6 06/37] thp: handle write-protection faults for file THP "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-01-26 17:00 +0100
  [PATCHv6 09/37] filemap: allocate huge page in pagecache_get_page(), if allowed "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:00 +0100
  [PATCHv6 34/37] ext4: make fallocate() operations work with huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:00 +0100
  [PATCHv6 31/37] ext4: handle writeback with huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:00 +0100
  [PATCHv6 10/37] filemap: handle huge pages in filemap_fdatawait_range() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 15/37] thp: do not threat slab pages as huge in hpage_{nr_pages,size,mask} "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 20/37] truncate: make truncate_inode_pages_range() aware about huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 13/37] mm: make write_cache_pages() work on huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 18/37] fs: make block_write_{begin,end}() be able to handle huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 32/37] ext4: make EXT4_IOC_MOVE_EXT work with huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 37/37] ext4, vfs: add huge= mount option "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 19/37] fs: make block_page_mkwrite() aware about huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 14/37] thp: introduce hpage_size() and hpage_mask() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 02/37] Revert "radix-tree: implement radix_tree_maybe_preload_order()" "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
    Re: [PATCHv6 02/37] Revert "radix-tree: implement  radix_tree_maybe_preload_order()" Matthew Wilcox <willy@infradead.org> - 2017-01-26 16:40 +0100
  [PATCHv6 26/37] ext4: handle huge pages in ext4_page_mkwrite() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 12/37] brd: make it handle huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 27/37] ext4: handle huge pages in __ext4_block_zero_page_range() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 29/37] ext4: handle huge pages in ext4_da_write_end() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 11/37] HACK: readahead: alloc huge pages, if allowed "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 33/37] ext4: fix SEEK_DATA/SEEK_HOLE for huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 24/37] ext4: make ext4_mpage_readpages() hugepage-aware "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 17/37] fs: make block_read_full_page() be able to read huge page "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 35/37] ext4: reserve larger jounral transaction for huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 07/37] filemap: allocate huge page in page_cache_read(), if allowed "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 23/37] mm: account huge pages to dirty, writaback, reclaimable, etc. "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 01/37] mm, shmem: swich huge tmpfs to multi-order radix-tree entries "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 04/37] mm, rmap: account file thp pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 22/37] mm, hugetlb: switch hugetlbfs to multi-order radix-tree entries "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 05/37] thp: try to free page's buffers before attempt split "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 28/37] ext4: make ext4_block_write_begin() aware about huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 08/37] filemap: handle huge pages in do_generic_file_read() "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 16/37] thp: make thp_get_unmapped_area() respect S_HUGE_MODE "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 21/37] truncate: make invalidate_inode_pages2_range() aware about huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100
  [PATCHv6 25/37] ext4: make ext4_writepage() work on huge pages "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> - 2017-01-26 13:10 +0100

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