On Tue, Apr 13, 2021 at 09:20:22PM -0400, Waiman Long wrote: > v3: > - Add missing "inline" qualifier to the alternate mod_obj_stock_state() > in patch 3. > - Remove redundant current_obj_stock() call in patch 5. > > v2: > - Fix bug found by test robot in patch 5. > - Update cover letter and commit logs. > > With the recent introduction of the new slab memory controller, we > eliminate the need for having separate kmemcaches for each memory > cgroup and reduce overall kernel memory usage. However, we also add > additional memory accounting overhead to each call of kmem_cache_alloc() > and kmem_cache_free(). > > For workloads that require a lot of kmemcache allocations and > de-allocations, they may experience performance regression as illustrated > in [1] and [2]. > > A simple kernel module that performs repeated loop of 100,000,000 > kmem_cache_alloc() and kmem_cache_free() of a 64-byte object at module > init time is used for benchmarking. The test was run on a CascadeLake > server with turbo-boosting disable to reduce run-to-run variation. > > With memory accounting disable, the run time was 2.848s. With memory > accounting enabled, the run times with the application of various > patches in the patchset were: > > Applied patches Run time Accounting overhead Overhead %age > --------------- -------- ------------------- ------------- > None 10.800s 7.952s 100.0% > 1-2 9.140s 6.292s 79.1% > 1-3 7.641s 4.793s 60.3% > 1-5 6.801s 3.953s 49.7% > > Note that this is the best case scenario where most updates happen only > to the percpu stocks. Real workloads will likely have a certain amount > of updates to the memcg charges and vmstats. So the performance benefit > will be less. > > It was found that a big part of the memory accounting overhead > was caused by the local_irq_save()/local_irq_restore() sequences in > updating local stock charge bytes and vmstat array, at least in x86 > systems. There are two such sequences in kmem_cache_alloc() and two > in kmem_cache_free(). This patchset tries to reduce the use of such > sequences as much as possible. In fact, it eliminates them in the common > case. Another part of this patchset to cache the vmstat data update in > the local stock as well which also helps. > > [1] https://lore.kernel.org/linux-mm/20210408193948.vfktg3azh2wrt56t@gabell/T/#u Hi Longman, Thank you for your patches. I rerun the benchmark with your patches, it seems that the reduction is small... The total duration of sendto() and recvfrom() system call during the benchmark are as follows. - sendto - v5.8 vanilla: 2576.056 msec (100%) - v5.12-rc7 vanilla: 2988.911 msec (116%) - v5.12-rc7 with your patches (1-5): 2984.307 msec (115%) - recvfrom - v5.8 vanilla: 2113.156 msec (100%) - v5.12-rc7 vanilla: 2305.810 msec (109%) - v5.12-rc7 with your patches (1-5): 2287.351 msec (108%) kmem_cache_alloc()/kmem_cache_free() are called around 1,400,000 times during the benchmark. I ran a loop in a kernel module as following. The duration is reduced by your patches actually. --- dummy_cache = KMEM_CACHE(dummy, SLAB_ACCOUNT); for (i = 0; i < 1400000; i++) { p = kmem_cache_alloc(dummy_cache, GFP_KERNEL); kmem_cache_free(dummy_cache, p); } --- - v5.12-rc7 vanilla: 110 msec (100%) - v5.12-rc7 with your patches (1-5): 85 msec (77%) It seems that the reduction is small for the benchmark though... Anyway, I can see your patches reduce the overhead. Please feel free to add: Tested-by: Masayoshi Mizuma <m.mizuma@xxxxxxxxxxxxxx> Thanks! Masa > [2] https://lore.kernel.org/lkml/20210114025151.GA22932@xsang-OptiPlex-9020/ > > Waiman Long (5): > mm/memcg: Pass both memcg and lruvec to mod_memcg_lruvec_state() > mm/memcg: Introduce obj_cgroup_uncharge_mod_state() > mm/memcg: Cache vmstat data in percpu memcg_stock_pcp > mm/memcg: Separate out object stock data into its own struct > mm/memcg: Optimize user context object stock access > > include/linux/memcontrol.h | 14 ++- > mm/memcontrol.c | 199 ++++++++++++++++++++++++++++++++----- > mm/percpu.c | 9 +- > mm/slab.h | 32 +++--- > 4 files changed, 196 insertions(+), 58 deletions(-) > > -- > 2.18.1 >
