kernel.git/mm/z3fold.c, branch linux-4.20.y

z3fold: fix possible reclaim races

2018-11-18T18:15:09Z

Reclaim and free can race on an object which is basically fine but in order for reclaim to be able to map "freed" object we need to encode object length in the handle. handle_to_chunks() is then introduced to extract object length from a handle and use it during mapping. Moreover, to avoid racing on a z3fold "headless" page release, we should not try to free that page in z3fold_free() if the reclaim bit is set. Also, in the unlikely case of trying to reclaim a page being freed, we should not proceed with that page. While at it, fix the page accounting in reclaim function. This patch supersedes "[PATCH] z3fold: fix reclaim lock-ups". Link: http://lkml.kernel.org/r/20181105162225.74e8837d03583a9b707cf559@gmail.com Signed-off-by: Vitaly Wool Signed-off-by: Jongseok Kim Reported-by-by: Jongseok Kim Reviewed-by: Snild Dolkow Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

z3fold: fix reclaim lock-ups

2018-05-12T00:28:45Z

Do not try to optimize in-page object layout while the page is under reclaim. This fixes lock-ups on reclaim and improves reclaim performance at the same time. [akpm@linux-foundation.org: coding-style fixes] Link: http://lkml.kernel.org/r/20180430125800.444cae9706489f412ad12621@gmail.com Signed-off-by: Vitaly Wool Reported-by: Guenter Roeck Tested-by: Guenter Roeck Cc: Cc: Matthew Wilcox Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/z3fold.c: use gfpflags_allow_blocking

2018-04-11T17:28:31Z

We have a perfectly good macro to determine whether the gfp flags allow you to sleep or not; use it instead of trying to infer it. Link: http://lkml.kernel.org/r/20180408062206.GC16007@bombadil.infradead.org Signed-off-by: Matthew Wilcox Reviewed-by: Andrew Morton Cc: Vitaly Wool Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

z3fold: fix memory leak

2018-04-11T17:28:31Z

In z3fold_create_pool(), the memory allocated by __alloc_percpu() is not released on the error path that pool->compact_wq , which holds the return value of create_singlethread_workqueue(), is NULL. This will result in a memory leak bug. [akpm@linux-foundation.org: fix oops on kzalloc() failure, check __alloc_percpu() retval] Link: http://lkml.kernel.org/r/1522803111-29209-1-git-send-email-wangxidong_97@163.com Signed-off-by: Xidong Wang Reviewed-by: Andrew Morton Cc: Vitaly Wool Cc: Mike Rapoport Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

z3fold: limit use of stale list for allocation

2018-04-06T04:36:25Z

Currently if z3fold couldn't find an unbuddied page it would first try to pull a page off the stale list. The problem with this approach is that we can't 100% guarantee that the page is not processed by the workqueue thread at the same time unless we run cancel_work_sync() on it, which we can't do if we're in an atomic context. So let's just limit stale list usage to non-atomic contexts only. Link: http://lkml.kernel.org/r/47ab51e7-e9c1-d30e-ab17-f734dbc3abce@gmail.com Signed-off-by: Vitaly Vul Reviewed-by: Andrew Morton Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: docs: fix parameter names mismatch

2018-02-07T02:32:48Z

There are several places where parameter descriptions do no match the actual code. Fix it. Link: http://lkml.kernel.org/r/1516700871-22279-3-git-send-email-rppt@linux.vnet.ibm.com Signed-off-by: Mike Rapoport Cc: Jonathan Corbet Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/z3fold.c: use kref to prevent page free/compact race

2017-11-18T00:10:00Z

There is a race in the current z3fold implementation between do_compact() called in a work queue context and the page release procedure when page's kref goes to 0. do_compact() may be waiting for page lock, which is released by release_z3fold_page_locked right before putting the page onto the "stale" list, and then the page may be freed as do_compact() modifies its contents. The mechanism currently implemented to handle that (checking the PAGE_STALE flag) is not reliable enough. Instead, we'll use page's kref counter to guarantee that the page is not released if its compaction is scheduled. It then becomes compaction function's responsibility to decrease the counter and quit immediately if the page was actually freed. Link: http://lkml.kernel.org/r/20171117092032.00ea56f42affbed19f4fcc6c@gmail.com Signed-off-by: Vitaly Wool Cc: Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

z3fold: fix stale list handling

2017-10-04T00:54:24Z

Fix the situation when clear_bit() is called for page->private before the page pointer is actually assigned. While at it, remove work_busy() check because it is costly and does not give 100% guarantee anyway. Signed-off-by: Vitaly Wool Cc: Dan Streetman Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

z3fold: fix potential race in z3fold_reclaim_page

2017-10-04T00:54:24Z

It is possible that on a (partially) unsuccessful page reclaim, kref_put() called in z3fold_reclaim_page() does not yield page release, but the page is released shortly afterwards by another thread. Then z3fold_reclaim_page() would try to list_add() that (released) page again which is obviously a bug. To avoid that, spin_lock() has to be taken earlier, before the kref_put() call mentioned earlier. Link: http://lkml.kernel.org/r/20170913162937.bfff21c7d12b12a5f47639fd@gmail.com Signed-off-by: Vitaly Wool Cc: Dan Streetman Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

z3fold: use per-cpu unbuddied lists

2017-09-07T00:27:30Z

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 Cc: Dan Streetman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds