Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> writes: > On Wed, Aug 31, 2016 at 08:17:24AM -0700, Huang, Ying wrote: >> 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? >> > > __GFP_BITS_SHIFT + 5 (AS_NO_WRITEBACK_TAGS) = 31 > > mapping->flags is a combination of AS and GFP flags so increasing > __GFP_BITS_SHIFT overflows mapping->flags on 32-bit as gfp_t is an > unsigned int. Got it! Thanks a lot! Best Regards, Huang, Ying -- 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>