Messages in this thread Patch in this message | | | From | "Kirill A. Shutemov" <> | Subject | [PATCHv2 18/41] HACK: readahead: alloc huge pages, if allowed | Date | Fri, 12 Aug 2016 21:38:01 +0300 |
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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 65ec288dc057..3cea3e8f1d3f 100644 --- a/mm/readahead.c +++ b/mm/readahead.c @@ -173,6 +173,21 @@ 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(); @@ -188,7 +203,7 @@ 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 -- 2.8.1
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