[PATCHv1, RFC 17/33] HACK: readahead: alloc huge pages, if allowed
From: Kirill A. Shutemov <hidden>
Date: 2016-07-26 00:35:19
Also in:
linux-ext4, linux-fsdevel, linux-mm, lkml
Subsystem:
memory management, page cache, the rest · Maintainers:
Andrew Morton, Matthew Wilcox, Linus Torvalds
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. Any suggestions are welcome. Signed-off-by: Kirill A. Shutemov <redacted> --- mm/readahead.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-)
diff --git a/mm/readahead.c b/mm/readahead.c
index 65ec288dc057..3d7742a687f2 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c@@ -173,6 +173,20 @@ int __do_page_cache_readahead(struct address_space *mapping, struct file *filp, if (page_offset > end_index) break; + if ((!page_idx || page_offset % HPAGE_PMD_NR == 0) && + 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();
@@ -188,7 +202,7 @@ 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
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2.8.1