Previously the mmap sequential readahead is triggered by updating ra->prev_pos on each page fault and compare it with current page offset. In the mosbench exim benchmark which does multi-threaded page faults on shared struct file, this is found to cause excessive cache line bouncing on tmpfs, which does not need readahead at all. So remove the ra->prev_pos recording, and instead tag PG_readahead to trigger the possible sequential readahead. It's not only more simple, but also will work more reliably on concurrent reads on shared struct file. Tested-by: Tim Chen Reported-by: Andi Kleen Signed-off-by: Wu Fengguang --- mm/filemap.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) --- linux-next.orig/mm/filemap.c 2011-04-23 16:52:21.000000000 +0800 +++ linux-next/mm/filemap.c 2011-04-24 09:59:08.000000000 +0800 @@ -1531,8 +1531,7 @@ static void do_sync_mmap_readahead(struc if (!ra->ra_pages) return; - if (VM_SequentialReadHint(vma) || - offset - 1 == (ra->prev_pos >> PAGE_CACHE_SHIFT)) { + if (VM_SequentialReadHint(vma)) { page_cache_sync_readahead(mapping, ra, file, offset, ra->ra_pages); return; @@ -1555,7 +1554,7 @@ static void do_sync_mmap_readahead(struc ra_pages = max_sane_readahead(ra->ra_pages); ra->start = max_t(long, 0, offset - ra_pages / 2); ra->size = ra_pages; - ra->async_size = 0; + ra->async_size = ra_pages / 4; ra_submit(ra, mapping, file); } @@ -1661,7 +1660,6 @@ retry_find: return VM_FAULT_SIGBUS; } - ra->prev_pos = (loff_t)offset << PAGE_CACHE_SHIFT; vmf->page = page; return ret | VM_FAULT_LOCKED; -- 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/