First, I wanted chime in to say as well: awesome report! This will be useful for us as well to refer to when deciding which allocator to use. I like the performance as well as the stability in the measurements with jemalloc. Looking at TCMaloc w/ TC128, didn't seem to stabilize on small write performance over the test period. Regarding the all-HDD or high density HDD nodes, is it certain these issues with tcmalloc don't apply, due to lower performance, or would it potentially be something that would manifest over a longer period of time (weeks/months) of running? I know we've seen some weirdness attributed to tcmalloc on our 10-disk 20-node cluster with HDD's & SSD journals, but it took a few weeks. Thanks, Stephen -----Original Message----- From: ceph-devel-owner@xxxxxxxxxxxxxxx [mailto:ceph-devel-owner@xxxxxxxxxxxxxxx] On Behalf Of Alexandre DERUMIER Sent: Wednesday, August 19, 2015 9:55 AM To: Somnath Roy Cc: Mark Nelson; ceph-devel Subject: Re: Ceph Hackathon: More Memory Allocator Testing << I think that tcmalloc have a fixed size (TCMALLOC_MAX_TOTAL_THREAD_CACHE_BYTES), and share it between all process. >>I think it is per tcmalloc instance loaded , so, at least with num_osds * num_tcmalloc_instance * TCMALLOC_MAX_TOTAL_THREAD_CACHE_BYTES in a box. What is num_tcmalloc_instance ? I think 1 osd process use a defined TCMALLOC_MAX_TOTAL_THREAD_CACHE_BYTES size ? I'm saying that, because I have exactly the same bug, client side, with librbd + tcmalloc + qemu + iothreads. When I defined too much iothread threads, I'm hitting the bug directly. (can reproduce 100%). Like the thread_cache size is divide by number of threads? ----- Mail original ----- De: "Somnath Roy" <Somnath.Roy@xxxxxxxxxxx> À: "aderumier" <aderumier@xxxxxxxxx>, "Mark Nelson" <mnelson@xxxxxxxxxx> Cc: "ceph-devel" <ceph-devel@xxxxxxxxxxxxxxx> Envoyé: Mercredi 19 Août 2015 18:27:30 Objet: RE: Ceph Hackathon: More Memory Allocator Testing << I think that tcmalloc have a fixed size (TCMALLOC_MAX_TOTAL_THREAD_CACHE_BYTES), and share it between all process. I think it is per tcmalloc instance loaded , so, at least with num_osds * num_tcmalloc_instance * TCMALLOC_MAX_TOTAL_THREAD_CACHE_BYTES in a box. Also, I think there is no point of increasing osd_op_threads as it is not in IO path anymore..Mark is using default 5:2 for shard:thread per shard.. But, yes, it could be related to number of threads OSDs are using, need to understand how jemalloc works..Also, there may be some tuning to reduce memory usage (?). Thanks & Regards Somnath -----Original Message----- From: ceph-devel-owner@xxxxxxxxxxxxxxx [mailto:ceph-devel-owner@xxxxxxxxxxxxxxx] On Behalf Of Alexandre DERUMIER Sent: Wednesday, August 19, 2015 9:06 AM To: Mark Nelson Cc: ceph-devel Subject: Re: Ceph Hackathon: More Memory Allocator Testing I was listening at the today meeting, and seem that the blocker to have jemalloc as default, is that it's used more memory by osd (around 300MB?), and some guys could have boxes with 60disks. I just wonder if the memory increase is related to osd_op_num_shards/osd_op_threads value ? Seem that as hackaton, the bench has been done on super big cpus boxed 36cores/72T, http://ceph.com/hackathon/2015-08-ceph-hammer-full-ssd.pptx with osd_op_threads = 32. I think that tcmalloc have a fixed size (TCMALLOC_MAX_TOTAL_THREAD_CACHE_BYTES), and share it between all process. Maybe jemalloc allocated memory by threads. (I think guys with 60disks box, dont use ssd, so low iops by osd, and they don't need a lot of threads by osd) ----- Mail original ----- De: "aderumier" <aderumier@xxxxxxxxx> À: "Mark Nelson" <mnelson@xxxxxxxxxx> Cc: "ceph-devel" <ceph-devel@xxxxxxxxxxxxxxx> Envoyé: Mercredi 19 Août 2015 16:01:28 Objet: Re: Ceph Hackathon: More Memory Allocator Testing Thanks Marc, Results are matching exactly what I have seen with tcmalloc 2.1 vs 2.4 vs jemalloc. and indeed tcmalloc, even with bigger cache, seem decrease over time. What is funny, is that I see exactly same behaviour client librbd side, with qemu and multiple iothreads. Switching both server and client to jemalloc give me best performance on small read currently. ----- Mail original ----- De: "Mark Nelson" <mnelson@xxxxxxxxxx> À: "ceph-devel" <ceph-devel@xxxxxxxxxxxxxxx> Envoyé: Mercredi 19 Août 2015 06:45:36 Objet: Ceph Hackathon: More Memory Allocator Testing Hi Everyone, One of the goals at the Ceph Hackathon last week was to examine how to improve Ceph Small IO performance. Jian Zhang presented findings showing a dramatic improvement in small random IO performance when Ceph is used with jemalloc. His results build upon Sandisk's original findings that the default thread cache values are a major bottleneck in TCMalloc 2.1. To further verify these results, we sat down at the Hackathon and configured the new performance test cluster that Intel generously donated to the Ceph community laboratory to run through a variety of tests with different memory allocator configurations. I've since written the results of those tests up in pdf form for folks who are interested. The results are located here: http://nhm.ceph.com/hackathon/Ceph_Hackathon_Memory_Allocator_Testing.pdf I want to be clear that many other folks have done the heavy lifting here. These results are simply a validation of the many tests that other folks have already done. Many thanks to Sandisk and others for figuring this out as it's a pretty big deal! Side note: Very little tuning other than swapping the memory allocator and a couple of quick and dirty ceph tunables were set during these tests. It's quite possible that higher IOPS will be achieved as we really start digging into the cluster and learning what the bottlenecks are. 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