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2017-09-06z3fold: use per-cpu unbuddied listsVitaly Wool
It's been noted that z3fold doesn't scale well when it's run in a large number of threads on many cores, which can be easily reproduced with fio 'randrw' test with --numjobs=32. E.g. the result for 1 cluster (4 cores) is: Run status group 0 (all jobs): READ: io=244785MB, aggrb=496883KB/s, minb=15527KB/s, ... WRITE: io=246735MB, aggrb=500841KB/s, minb=15651KB/s, ... While for 8 cores (2 clusters) the result is: Run status group 0 (all jobs): READ: io=244785MB, aggrb=265942KB/s, minb=8310KB/s, ... WRITE: io=246735MB, aggrb=268060KB/s, minb=8376KB/s, ... The bottleneck here is the pool lock which many threads become waiting upon. To reduce that spin lock contention, z3fold can operate only on the lists local to the current CPU whenever possible. Due to the nature of z3fold unbuddied list handling (it only takes the first entry off the list on a hot path), if the z3fold pool is big enough and balanced well enough, limiting search to only local unbuddied list doesn't lead to a significant compression ratio degrade (2.57x vs 2.65x in our measurements). This patch also introduces two worker threads: one for async in-page object layout optimization and one for releasing freed pages. This is done to speed up z3fold_free() which is often on a hot path. The fio results for 8-core case are now the following: Run status group 0 (all jobs): READ: io=244785MB, aggrb=1568.3MB/s, minb=50182KB/s, ... WRITE: io=246735MB, aggrb=1580.8MB/s, minb=50582KB/s, ... So we're in for almost 6x performance increase. Link: http://lkml.kernel.org/r/20170806181443.f9b65018f8bde25ef990f9e8@gmail.com Signed-off-by: Vitaly Wool <vitalywool@gmail.com> Cc: Dan Streetman <ddstreet@ieee.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-04-13z3fold: fix page locking in z3fold_alloc()Vitaly Wool
Stress testing of the current z3fold implementation on a 8-core system revealed it was possible that a z3fold page deleted from its unbuddied list in z3fold_alloc() would be put on another unbuddied list by z3fold_free() while z3fold_alloc() is still processing it. This has been introduced with commit 5a27aa822 ("z3fold: add kref refcounting") due to the removal of special handling of a z3fold page not on any list in z3fold_free(). To fix this, the z3fold page lock should be taken in z3fold_alloc() before the pool lock is released. To avoid deadlocking, we just try to lock the page as soon as we get a hold of it, and if trylock fails, we drop this page and take the next one. Signed-off-by: Vitaly Wool <vitalywool@gmail.com> Cc: Dan Streetman <ddstreet@ieee.org> Cc: <Oleksiy.Avramchenko@sony.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-03-16z3fold: fix spinlock unlocking in page reclaimVitaly Wool
Commmit 5a27aa822029 ("z3fold: add kref refcounting") introduced a bug in z3fold_reclaim_page() with function exit that may leave pool->lock spinlock held. Here comes the trivial fix. Fixes: 5a27aa822029 ("z3fold: add kref refcounting") Link: http://lkml.kernel.org/r/20170311222239.7b83d8e7ef1914e05497649f@gmail.com Reported-by: Alexey Khoroshilov <khoroshilov@ispras.ru> Signed-off-by: Vitaly Wool <vitalywool@gmail.com> Cc: Dan Streetman <ddstreet@ieee.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-02-24z3fold: add kref refcountingVitaly Wool
With both coming and already present locking optimizations, introducing kref to reference-count z3fold objects is the right thing to do. Moreover, it makes buddied list no longer necessary, and allows for a simpler handling of headless pages. [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/20170131214650.8ea78033d91ded233f552bc0@gmail.com Signed-off-by: Vitaly Wool <vitalywool@gmail.com> Reviewed-by: Dan Streetman <ddstreet@ieee.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-02-24z3fold: use per-page spinlockVitaly Wool
Most of z3fold operations are in-page, such as modifying z3fold page header or moving z3fold objects within a page. Taking per-pool spinlock to protect per-page objects is therefore suboptimal, and the idea of having a per-page spinlock (or rwlock) has been around for some time. This patch implements spinlock-based per-page locking mechanism which is lightweight enough to normally fit ok into the z3fold header. Link: http://lkml.kernel.org/r/20170131214438.433e0a5fda908337b63206d3@gmail.com Signed-off-by: Vitaly Wool <vitalywool@gmail.com> Reviewed-by: Dan Streetman <ddstreet@ieee.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-02-24z3fold: extend compaction functionVitaly Wool
z3fold_compact_page() currently only handles the situation when there's a single middle chunk within the z3fold page. However it may be worth it to move middle chunk closer to either first or last chunk, whichever is there, if the gap between them is big enough. This patch adds the relevant code, using BIG_CHUNK_GAP define as a threshold for middle chunk to be worth moving. Link: http://lkml.kernel.org/r/20170131214334.c4f3eac9a477af0fa9a22c46@gmail.com Signed-off-by: Vitaly Wool <vitalywool@gmail.com> Reviewed-by: Dan Streetman <ddstreet@ieee.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-02-24z3fold: fix header size related issuesVitaly Wool
Currently the whole kernel build will be stopped if the size of struct z3fold_header is greater than the size of one chunk, which is 64 bytes by default. This patch instead defines the offset for z3fold objects as the size of the z3fold header in chunks. Fixed also are the calculation of num_free_chunks() and the address to move the middle chunk to in case of in-page compaction in z3fold_compact_page(). Link: http://lkml.kernel.org/r/20170131214057.d98677032bc7b1c6c59a80c9@gmail.com Signed-off-by: Vitaly Wool <vitalywool@gmail.com> Reviewed-by: Dan Streetman <ddstreet@ieee.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-02-24z3fold: make pages_nr atomicVitaly Wool
Convert pages_nr per-pool counter to atomic64_t. Link: http://lkml.kernel.org/r/20170131213946.b828676ab17bbea42022c213@gmail.com Signed-off-by: Vitaly Wool <vitalywool@gmail.com> Reviewed-by: Dan Streetman <ddstreet@ieee.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-02-22mm/z3fold.c: limit first_num to the actual range of possible buddy indexeszhong jiang
At present, Tying the first_num size to NCHUNKS_ORDER is confusing. the number of chunks is completely unrelated to the number of buddies. The patch limits the first_num to actual range of possible buddy indexes. and that is more reasonable and obvious without functional change. Link: http://lkml.kernel.org/r/1476776569-29504-1-git-send-email-zhongjiang@huawei.com Signed-off-by: zhong jiang <zhongjiang@huawei.com> Suggested-by: Dan Streetman <ddstreet@ieee.org> Acked-by: Dan Streetman <ddstreet@ieee.org> Acked-by: Vitaly Wool <vitalywool@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-06-03mm/z3fold.c: avoid modifying HEADLESS page and minor cleanupVitaly Wool
Fix erroneous z3fold header access in a HEADLESS page in reclaim function, and change one remaining direct handle-to-buddy conversion to use the appropriate helper. Link: http://lkml.kernel.org/r/5748706F.9020208@gmail.com Signed-off-by: Vitaly Wool <vitalywool@gmail.com> Reviewed-by: Dan Streetman <ddstreet@ieee.org> Cc: Seth Jennings <sjenning@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-05-20z3fold: the 3-fold allocator for compressed pagesVitaly Wool
This patch introduces z3fold, a special purpose allocator for storing compressed pages. It is designed to store up to three compressed pages per physical page. It is a ZBUD derivative which allows for higher compression ratio keeping the simplicity and determinism of its predecessor. This patch comes as a follow-up to the discussions at the Embedded Linux Conference in San-Diego related to the talk [1]. The outcome of these discussions was that it would be good to have a compressed page allocator as stable and deterministic as zbud with with higher compression ratio. To keep the determinism and simplicity, z3fold, just like zbud, always stores an integral number of compressed pages per page, but it can store up to 3 pages unlike zbud which can store at most 2. Therefore the compression ratio goes to around 2.6x while zbud's one is around 1.7x. The patch is based on the latest linux.git tree. This version has been updated after testing on various simulators (e.g. ARM Versatile Express, MIPS Malta, x86_64/Haswell) and basing on comments from Dan Streetman [3]. [1] https://openiotelc2016.sched.org/event/6DAC/swapping-and-embedded-compression-relieves-the-pressure-vitaly-wool-softprise-consulting-ou [2] https://lkml.org/lkml/2016/4/21/799 [3] https://lkml.org/lkml/2016/5/4/852 Link: http://lkml.kernel.org/r/20160509151753.ec3f9fda3c9898d31ff52a32@gmail.com Signed-off-by: Vitaly Wool <vitalywool@gmail.com> Cc: Seth Jennings <sjenning@redhat.com> Cc: Dan Streetman <ddstreet@ieee.org> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>