Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> writes: > On Tue, Aug 30, 2016 at 10:28:09AM -0700, Huang, Ying wrote: >> From: Huang Ying <ying.huang@xxxxxxxxx> >> >> File pages use a set of radix tree tags (DIRTY, TOWRITE, WRITEBACK, >> etc.) to accelerate finding the pages with a specific tag in the radix >> tree during inode writeback. But for anonymous pages in the swap >> cache, there is no inode writeback. So there is no need to find the >> pages with some writeback tags in the radix tree. It is not necessary >> to touch radix tree writeback tags for pages in the swap cache. >> >> Per Rik van Riel's suggestion, a new flag AS_NO_WRITEBACK_TAGS is >> introduced for address spaces which don't need to update the writeback >> tags. The flag is set for swap caches. It may be used for DAX file >> systems, etc. >> >> With this patch, the swap out bandwidth improved 22.3% (from ~1.2GB/s to >> ~ 1.48GBps) in the vm-scalability swap-w-seq test case with 8 processes. >> The test is done on a Xeon E5 v3 system. The swap device used is a RAM >> simulated PMEM (persistent memory) device. The improvement comes from >> the reduced contention on the swap cache radix tree lock. To test >> sequential swapping out, the test case uses 8 processes, which >> sequentially allocate and write to the anonymous pages until RAM and >> part of the swap device is used up. >> >> Details of comparison is as follow, >> >> base base+patch >> ---------------- -------------------------- >> %stddev %change %stddev >> \ | \ >> 2506952 ± 2% +28.1% 3212076 ± 7% vm-scalability.throughput >> 1207402 ± 7% +22.3% 1476578 ± 6% vmstat.swap.so >> 10.86 ± 12% -23.4% 8.31 ± 16% perf-profile.cycles-pp._raw_spin_lock_irq.__add_to_swap_cache.add_to_swap_cache.add_to_swap.shrink_page_list >> 10.82 ± 13% -33.1% 7.24 ± 14% perf-profile.cycles-pp._raw_spin_lock_irqsave.__remove_mapping.shrink_page_list.shrink_inactive_list.shrink_zone_memcg >> 10.36 ± 11% -100.0% 0.00 ± -1% perf-profile.cycles-pp._raw_spin_lock_irqsave.__test_set_page_writeback.bdev_write_page.__swap_writepage.swap_writepage >> 10.52 ± 12% -100.0% 0.00 ± -1% perf-profile.cycles-pp._raw_spin_lock_irqsave.test_clear_page_writeback.end_page_writeback.page_endio.pmem_rw_page >> > > I didn't see anything wrong with the patch but it's worth highlighting > that this hunk means we are now out of GFP bits. Sorry, I don't know whether I understand your words. It is something about, __GFP_BITS_SHIFT == 26 So remainning bits in mapping_flags is 6. And now the latest bit is used for the flag introduced in the patch? Best Regards, Huang, Ying >> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h >> index 66a1260..2f5a65dd 100644 >> --- a/include/linux/pagemap.h >> +++ b/include/linux/pagemap.h >> @@ -25,6 +25,8 @@ enum mapping_flags { >> AS_MM_ALL_LOCKS = __GFP_BITS_SHIFT + 2, /* under mm_take_all_locks() */ >> AS_UNEVICTABLE = __GFP_BITS_SHIFT + 3, /* e.g., ramdisk, SHM_LOCK */ >> AS_EXITING = __GFP_BITS_SHIFT + 4, /* final truncate in progress */ >> + /* writeback related tags are not used */ >> + AS_NO_WRITEBACK_TAGS = __GFP_BITS_SHIFT + 5, >> }; >> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>