On 15.2.2015 21:13, Andres Freund wrote: > On 2015-02-15 21:07:13 +0100, Tomas Vondra wrote: > >> malloc() does that only for allocations over MAP_THRESHOLD, which >> is 128kB by default. Vast majority of blocks we allocate are <= >> 8kB, so mmap() almost never happens. > > The problem is that mmap() is, to my knowledge, noticeably more > expensive than sbrk(). Especially with concurrent workloads. Which is > why the malloc/libc authors chose to use sbrk ...
Any ideas how to simulate such workloads? None of the tests I've done suggested such issue exists. > IIRC glibc malloc also batches several allocation into mmap()ed > areas after some time. Maybe, there's certainly a lot of such optimizations in libc. But how do you return memory to system in that case? -- Tomas Vondra http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
