Messages in this thread | | | Date | Mon, 13 Apr 2009 12:44:57 -0700 | Subject | [V4][PATCH 0/4]page fault retry with NOPAGE_RETRY | From | Ying Han <> |
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page fault retry with NOPAGE_RETRY Allow major faults to drop the mmap_sem read lock while waiting for synchronous disk read. This allows another thread which wishes to grab down_write(mmap_sem) to proceed while the current is waiting the disk IO.
The patch replace the 'write' with flag of handle_mm_fault() to FAULT_FLAG_RETRY as identify that the caller can tolerate the retry in the filemap_fault call patch.
Compiled and booted on x86_64. (Andrew: can you help on other arches )
changelog[v4]: - split the patch into four parts. the first two patches is a cleanup of Linus "untested" patch, which replace the boolen "writeaccess" to be a flag in handle_mm_fault. and the last two patches add the FAULT_FLAG_RETRY support. - include all arches cleanups. - add more comments as Andrew suggested. - cleanups as Fengguang Wu suggested.
changelog[v3]: - applied fixes and cleanups from Wu Fengguang. filemap VM_FAULT_RETRY fixes [PATCH 01/14] mm: fix find_lock_page_retry() return value parsing [PATCH 02/14] mm: fix major/minor fault accounting on retried fault [PATCH 04/14] mm: reduce duplicate page fault code [PATCH 05/14] readahead: account mmap_miss for VM_FAULT_RETRY
- split the patch into two parts. first part includes FAULT_FLAG_RETRY support with no current user change. second part includes individual per-architecture cleanups that enable FAULT_FLAG_RETRY. currently there are mainly two users for handle_mm_fault, we enable FAULT_FLAG_RETRY for actual fault handler and leave get_user_pages unchanged.
changelog[v2]: - reduce the runtime overhead by extending the 'write' flag of handle_mm_fault() to indicate the retry hint. - add another two branches in filemap_fault with retry logic. - replace find_lock_page with find_lock_page_retry to make the code cleaner.
Benchmarks: case 1. one application has a high count of threads each faulting in different pages of a hugefile. Benchmark indicate that this double data structure walking in case of major fault results in << 1% performance hit.
case 2. add another thread in the above application which in a tight loop of mmap()/munmap(). Here we measure loop count in the new thread while other threads doing the same amount of work as case one. we got << 3% performance hit on the Complete Time(benchmark value for case one) and 10% performance improvement on the mmap()/munmap() counter.
This patch helps a lot in cases we have writer which is waitting behind all readers, so it could execute much faster.
benchmarks from Wufengguang: Just tested the sparse-random-read-on-sparse-file case, and found the performance impact to be 0.4% (8.706s vs 8.744s) in the worst case. Kind of acceptable.
without FAULT_FLAG_RETRY: iotrace.rb --load stride-100 --mplay /mnt/btrfs-ram/sparse 3.28s user 5.39s system 99% cpu 8.692 total iotrace.rb --load stride-100 --mplay /mnt/btrfs-ram/sparse 3.17s user 5.54s system 99% cpu 8.742 total iotrace.rb --load stride-100 --mplay /mnt/btrfs-ram/sparse 3.18s user 5.48s system 99% cpu 8.684 total
FAULT_FLAG_RETRY: iotrace.rb --load stride-100 --mplay /mnt/btrfs-ram/sparse 3.18s user 5.63s system 99% cpu 8.825 total iotrace.rb --load stride-100 --mplay /mnt/btrfs-ram/sparse 3.22s user 5.47s system 99% cpu 8.718 total iotrace.rb --load stride-100 --mplay /mnt/btrfs-ram/sparse 3.13s user 5.55s system 99% cpu 8.690 total
In the above faked workload, the mmap read page offsets are loaded from stride-100 and performed on /mnt/btrfs-ram/sparse, which are created by:
seq 0 100 1000000 > stride-100 dd if=/dev/zero of=/mnt/btrfs-ram/sparse bs=1M count=1 seek=1024000
Signed-off-by: Mike Waychison <mikew@google.com> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Ying Han <yinghan@google.com>
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