On 15.2.2015 20:56, Heikki Linnakangas wrote: > On 02/15/2015 08:57 PM, Tomas Vondra wrote: >> One of the wilder ideas (I mentined beer was involved!) was a memory >> allocator based on mmap [2], bypassing the libc malloc implementation >> altogether. mmap() has some nice features (e.g. no issues with returning >> memory back to the kernel, which may be problem with sbrk). So I hacked >> a bit and switched the AllocSet implementation to mmap(). > > glibc's malloc() also uses mmap() for larger allocations. Precisely > because those allocations can then be handed back to the OS. I don't > think we'd want to use mmap() for small allocations either. Let's not > re-invent malloc()..
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. At least that's my understanding, I may be wrong of course. > > - Heikki > -- 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
