Auto-detect sequential mmap reads and do readahead for them. The sequential mmap readahead will be triggered when - sync readahead: it's a major fault and (prev_offset == offset-1); - async readahead: minor fault on PG_readahead page with valid readahead state. The benefits of doing readahead instead of read-around: - less I/O wait thanks to async readahead - double real I/O size and no more cache hits The single stream case is improved a little. For 100,000 sequential mmap reads: user system cpu total (1-1) plain -mm, 128KB readaround: 3.224 2.554 48.40% 11.838 (1-2) plain -mm, 256KB readaround: 3.170 2.392 46.20% 11.976 (2) patched -mm, 128KB readahead: 3.117 2.448 47.33% 11.607 The patched (2) has smallest total time, since it has no cache hit overheads and less I/O block time(thanks to async readahead). Here the I/O size makes no much difference, since there's only one single stream. Note that (1-1)'s real I/O size is 64KB and (1-2)'s real I/O size is 128KB, since the half of the read-around pages will be readahead cache hits. This is going to make _real_ differences for _concurrent_ IO streams. Cc: Nick Piggin Cc: Linus Torvalds Signed-off-by: Wu Fengguang --- mm/filemap.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- mm.orig/mm/filemap.c +++ mm/mm/filemap.c @@ -1471,7 +1471,8 @@ static void do_sync_mmap_readahead(struc if (VM_RandomReadHint(vma)) return; - if (VM_SequentialReadHint(vma)) { + if (VM_SequentialReadHint(vma) || + offset - 1 == (ra->prev_pos >> PAGE_CACHE_SHIFT)) { page_cache_sync_readahead(mapping, ra, file, offset, 1); return; } -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/