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On Tue, Feb 10, 2015 at 08:27:03PM +0000, Mel Gorman wrote: > Trimming heaps is a balance between saving memory and the system overhead > required to update page tables and discard allocated pages. The malloc > option M_TRIM_THRESHOLD is a tunable that users are meant to use to decide > where this balance point is but it is only applied to the main arena. > > For scalability reasons, glibc malloc has per-thread heaps but these are > shrunk with madvise() if there is one page free at the top of the heap. > In some circumstances this can lead to high system overhead if a thread > has a control flow like > > while (data_to_process) { > buf = malloc(large_size); > do_stuff(); > free(buf); > } > > For a large size, the free() will call madvise (pagetable teardown, page > free and TLB flush) every time followed immediately by a malloc (fault, > kernel page alloc, zeroing and charge accounting). The kernel overhead > can dominate such a workload. > > This patch allows the user to tune when madvise gets called by applying > the trim threshold to the per-thread heaps. Thanks for fixing this. I consider this a bug, since the complementary tunable MALLOC_MMAP_THRESHOLD_ does get applied to non-main arenas. > diff --git a/ChangeLog b/ChangeLog > index dc1ed1ba1249..b860b2fe1850 100644 > --- a/ChangeLog > +++ b/ChangeLog > @@ -1,3 +1,8 @@ > +2015-02-10 Mel Gorman <mgorman@suse.de> > + > + * malloc/arena.c (free): Apply trim threshold to per-thread heaps > + as well as the main arena. > + > 2015-02-06 Carlos O'Donell <carlos@systemhalted.org> This should not be in a diff since it won't always apply to the current tree cleanly. Please file a bug for this (since it is an unintended inconsistency) and I'll push it for you. Thanks, Siddhesh
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