On Mon, Jul 16, 2018 at 3:30 PM Andrew Dunstan <andrew.duns...@2ndquadrant.com> wrote: > > > > On 07/16/2018 10:34 AM, Claudio Freire wrote: > > On Fri, Jul 13, 2018 at 5:43 PM Andrew Dunstan > > <andrew.duns...@2ndquadrant.com> wrote: > >> > >> > >> On 07/13/2018 09:44 AM, Heikki Linnakangas wrote: > >>> On 13/07/18 01:39, Andrew Dunstan wrote: > >>>> On 07/12/2018 06:34 PM, Alvaro Herrera wrote: > >>>>> On 2018-Jul-12, Andrew Dunstan wrote: > >>>>> > >>>>>> I fully understand. I think this needs to go back to "Waiting on > >>>>>> Author". > >>>>> Why? Heikki's patch applies fine and passes the regression tests. > >>>> Well, I understood Claudio was going to do some more work (see > >>>> upthread). > >>> Claudio raised a good point, that doing small pallocs leads to > >>> fragmentation, and in particular, it might mean that we can't give > >>> back the memory to the OS. The default glibc malloc() implementation > >>> has a threshold of 4 or 32 MB or something like that - allocations > >>> larger than the threshold are mmap()'d, and can always be returned to > >>> the OS. I think a simple solution to that is to allocate larger > >>> chunks, something like 32-64 MB at a time, and carve out the > >>> allocations for the nodes from those chunks. That's pretty > >>> straightforward, because we don't need to worry about freeing the > >>> nodes in retail. Keep track of the current half-filled chunk, and > >>> allocate a new one when it fills up. > >> > >> Google seems to suggest the default threshold is much lower, like 128K. > >> Still, making larger allocations seems sensible. Are you going to work > >> on that? > > Below a few MB the threshold is dynamic, and if a block bigger than > > 128K but smaller than the higher threshold (32-64MB IIRC) is freed, > > the dynamic threshold is set to the size of the freed block. > > > > See M_MMAP_MAX and M_MMAP_THRESHOLD in the man page for mallopt[1] > > > > So I'd suggest allocating blocks bigger than M_MMAP_MAX. > > > > [1] http://man7.org/linux/man-pages/man3/mallopt.3.html > > > That page says: > > M_MMAP_MAX > This parameter specifies the maximum number of allocation > requests that may be simultaneously serviced using mmap(2). > This parameter exists because some systems have a limited > number of internal tables for use by mmap(2), and using more > than a few of them may degrade performance. > > The default value is 65,536, a value which has no special > significance and which serves only as a safeguard. Setting > this parameter to 0 disables the use of mmap(2) for servicing > large allocation requests. > > > I'm confused about the relevance.
It isn't relevant. See my next message, it should have read DEFAULT_MMAP_THRESHOLD_MAX.