lwn.git/mm, branch v3.14.21

mm: don't pointlessly use BUG_ON() for sanity check

2014-10-09T19:21:29+00:00

commit 50f5aa8a9b248fa4262cf379863ec9a531b49737 upstream. BUG_ON() is a big hammer, and should be used _only_ if there is some major corruption that you cannot possibly recover from, making it imperative that the current process (and possibly the whole machine) be terminated with extreme prejudice. The trivial sanity check in the vmacache code is *not* such a fatal error. Recovering from it is absolutely trivial, and using BUG_ON() just makes it harder to debug for no actual advantage. To make matters worse, the placement of the BUG_ON() (only if the range check matched) actually makes it harder to hit the sanity check to begin with, so _if_ there is a bug (and we just got a report from Srivatsa Bhat that this can indeed trigger), it is harder to debug not just because the machine is possibly dead, but because we don't have better coverage. BUG_ON() must *die*. Maybe we should add a checkpatch warning for it, because it is simply just about the worst thing you can ever do if you hit some "this cannot happen" situation. Reported-by: Srivatsa S. Bhat Cc: Davidlohr Bueso Cc: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Mel Gorman Signed-off-by: Greg Kroah-Hartman

mm: per-thread vma caching

2014-10-09T19:21:29+00:00

commit 615d6e8756c87149f2d4c1b93d471bca002bd849 upstream. This patch is a continuation of efforts trying to optimize find_vma(), avoiding potentially expensive rbtree walks to locate a vma upon faults. The original approach (https://lkml.org/lkml/2013/11/1/410), where the largest vma was also cached, ended up being too specific and random, thus further comparison with other approaches were needed. There are two things to consider when dealing with this, the cache hit rate and the latency of find_vma(). Improving the hit-rate does not necessarily translate in finding the vma any faster, as the overhead of any fancy caching schemes can be too high to consider. We currently cache the last used vma for the whole address space, which provides a nice optimization, reducing the total cycles in find_vma() by up to 250%, for workloads with good locality. On the other hand, this simple scheme is pretty much useless for workloads with poor locality. Analyzing ebizzy runs shows that, no matter how many threads are running, the mmap_cache hit rate is less than 2%, and in many situations below 1%. The proposed approach is to replace this scheme with a small per-thread cache, maximizing hit rates at a very low maintenance cost. Invalidations are performed by simply bumping up a 32-bit sequence number. The only expensive operation is in the rare case of a seq number overflow, where all caches that share the same address space are flushed. Upon a miss, the proposed replacement policy is based on the page number that contains the virtual address in question. Concretely, the following results are seen on an 80 core, 8 socket x86-64 box: 1) System bootup: Most programs are single threaded, so the per-thread scheme does improve ~50% hit rate by just adding a few more slots to the cache. +----------------+----------+------------------+ | caching scheme | hit-rate | cycles (billion) | +----------------+----------+------------------+ | baseline | 50.61% | 19.90 | | patched | 73.45% | 13.58 | +----------------+----------+------------------+ 2) Kernel build: This one is already pretty good with the current approach as we're dealing with good locality. +----------------+----------+------------------+ | caching scheme | hit-rate | cycles (billion) | +----------------+----------+------------------+ | baseline | 75.28% | 11.03 | | patched | 88.09% | 9.31 | +----------------+----------+------------------+ 3) Oracle 11g Data Mining (4k pages): Similar to the kernel build workload. +----------------+----------+------------------+ | caching scheme | hit-rate | cycles (billion) | +----------------+----------+------------------+ | baseline | 70.66% | 17.14 | | patched | 91.15% | 12.57 | +----------------+----------+------------------+ 4) Ebizzy: There's a fair amount of variation from run to run, but this approach always shows nearly perfect hit rates, while baseline is just about non-existent. The amounts of cycles can fluctuate between anywhere from ~60 to ~116 for the baseline scheme, but this approach reduces it considerably. For instance, with 80 threads: +----------------+----------+------------------+ | caching scheme | hit-rate | cycles (billion) | +----------------+----------+------------------+ | baseline | 1.06% | 91.54 | | patched | 99.97% | 14.18 | +----------------+----------+------------------+ [akpm@linux-foundation.org: fix nommu build, per Davidlohr] [akpm@linux-foundation.org: document vmacache_valid() logic] [akpm@linux-foundation.org: attempt to untangle header files] [akpm@linux-foundation.org: add vmacache_find() BUG_ON] [hughd@google.com: add vmacache_valid_mm() (from Oleg)] [akpm@linux-foundation.org: coding-style fixes] [akpm@linux-foundation.org: adjust and enhance comments] Signed-off-by: Davidlohr Bueso Reviewed-by: Rik van Riel Acked-by: Linus Torvalds Reviewed-by: Michel Lespinasse Cc: Oleg Nesterov Tested-by: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Mel Gorman Signed-off-by: Greg Kroah-Hartman

vmscan: reclaim_clean_pages_from_list() must use mod_zone_page_state()

2014-10-09T19:21:29+00:00

commit 83da7510058736c09a14b9c17ec7d851940a4332 upstream. Seems to be called with preemption enabled. Therefore it must use mod_zone_page_state instead. Signed-off-by: Christoph Lameter Reported-by: Grygorii Strashko Tested-by: Grygorii Strashko Cc: Tejun Heo Cc: Santosh Shilimkar Cc: Ingo Molnar Cc: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Mel Gorman Signed-off-by: Greg Kroah-Hartman

mm: vmscan: shrink_slab: rename max_pass -> freeable

2014-10-09T19:21:29+00:00

commit d5bc5fd3fcb7b8dfb431694a8c8052466504c10c upstream. The name `max_pass' is misleading, because this variable actually keeps the estimate number of freeable objects, not the maximal number of objects we can scan in this pass, which can be twice that. Rename it to reflect its actual meaning. Signed-off-by: Vladimir Davydov Acked-by: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Mel Gorman Signed-off-by: Greg Kroah-Hartman

mm: vmscan: respect NUMA policy mask when shrinking slab on direct reclaim

2014-10-09T19:21:29+00:00

commit 99120b772b52853f9a2b829a21dd44d9b20558f1 upstream. When direct reclaim is executed by a process bound to a set of NUMA nodes, we should scan only those nodes when possible, but currently we will scan kmem from all online nodes even if the kmem shrinker is NUMA aware. That said, binding a process to a particular NUMA node won't prevent it from shrinking inode/dentry caches from other nodes, which is not good. Fix this. Signed-off-by: Vladimir Davydov Cc: Mel Gorman Cc: Michal Hocko Cc: Johannes Weiner Cc: Rik van Riel Cc: Dave Chinner Cc: Glauber Costa Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Mel Gorman Signed-off-by: Greg Kroah-Hartman

mm/filemap.c: avoid always dirtying mapping->flags on O_DIRECT

2014-10-09T19:21:29+00:00

commit 7fcbbaf18392f0b17c95e2f033c8ccf87eecde1d upstream. In some testing I ran today (some fio jobs that spread over two nodes), we end up spending 40% of the time in filemap_check_errors(). That smells fishy. Looking further, this is basically what happens: blkdev_aio_read() generic_file_aio_read() filemap_write_and_wait_range() if (!mapping->nr_pages) filemap_check_errors() and filemap_check_errors() always attempts two test_and_clear_bit() on the mapping flags, thus dirtying it for every single invocation. The patch below tests each of these bits before clearing them, avoiding this issue. In my test case (4-socket box), performance went from 1.7M IOPS to 4.0M IOPS. Signed-off-by: Jens Axboe Acked-by: Jeff Moyer Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Mel Gorman Signed-off-by: Greg Kroah-Hartman

mm: optimize put_mems_allowed() usage

2014-10-09T19:21:28+00:00

commit d26914d11751b23ca2e8747725f2cae10c2f2c1b upstream. Since put_mems_allowed() is strictly optional, its a seqcount retry, we don't need to evaluate the function if the allocation was in fact successful, saving a smp_rmb some loads and comparisons on some relative fast-paths. Since the naming, get/put_mems_allowed() does suggest a mandatory pairing, rename the interface, as suggested by Mel, to resemble the seqcount interface. This gives us: read_mems_allowed_begin() and read_mems_allowed_retry(), where it is important to note that the return value of the latter call is inverted from its previous incarnation. Signed-off-by: Peter Zijlstra Signed-off-by: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Mel Gorman Signed-off-by: Greg Kroah-Hartman

mm/readahead.c: fix readahead failure for memoryless NUMA nodes and limit readahead pages

2014-10-09T19:21:28+00:00

commit 6d2be915e589b58cb11418cbe1f22ff90732b6ac upstream. Currently max_sane_readahead() returns zero on the cpu whose NUMA node has no local memory which leads to readahead failure. Fix this readahead failure by returning minimum of (requested pages, 512). Users running applications on a memory-less cpu which needs readahead such as streaming application see considerable boost in the performance. Result: fadvise experiment with FADV_WILLNEED on a PPC machine having memoryless CPU with 1GB testfile (12 iterations) yielded around 46.66% improvement. fadvise experiment with FADV_WILLNEED on a x240 machine with 1GB testfile 32GB* 4G RAM numa machine (12 iterations) showed no impact on the normal NUMA cases w/ patch. Kernel Avg Stddev base 7.4975 3.92% patched 7.4174 3.26% [Andrew: making return value PAGE_SIZE independent] Suggested-by: Linus Torvalds Signed-off-by: Raghavendra K T Acked-by: Jan Kara Cc: Wu Fengguang Cc: David Rientjes Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Mel Gorman Signed-off-by: Greg Kroah-Hartman

mm, compaction: ignore pageblock skip when manually invoking compaction

2014-10-09T19:21:28+00:00

commit 91ca9186484809c57303b33778d841cc28f696ed upstream. The cached pageblock hint should be ignored when triggering compaction through /proc/sys/vm/compact_memory so all eligible memory is isolated. Manually invoking compaction is known to be expensive, there's no need to skip pageblocks based on heuristics (mainly for debugging). Signed-off-by: David Rientjes Acked-by: Mel Gorman Cc: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Mel Gorman Signed-off-by: Greg Kroah-Hartman

mm, compaction: determine isolation mode only once

2014-10-09T19:21:28+00:00

commit da1c67a76f7cf2b3404823d24f9f10fa91aa5dc5 upstream. The conditions that control the isolation mode in isolate_migratepages_range() do not change during the iteration, so extract them out and only define the value once. This actually does have an effect, gcc doesn't optimize it itself because of cc->sync. Signed-off-by: David Rientjes Cc: Mel Gorman Acked-by: Rik van Riel Acked-by: Vlastimil Babka Cc: Joonsoo Kim Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Mel Gorman Signed-off-by: Greg Kroah-Hartman