Date: Thu, 12 Apr 2018 09:26:29 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: [RFC PATCH] reduce severity of ldso reclaim_gaps hack On Thu, Apr 12, 2018 at 09:40:23AM +0300, Alexander Monakov wrote: > On Thu, 12 Apr 2018, Rich Felker wrote: > > > > This does not seem necessary. Free chunks in the last bin can be > > > > larger than MMAP_THRESHOLD; they're just broken up to satisfy > > > > allocations. Of course it's unlikely to happen anyway. > > > > > > Do such oversized chunks appear in normal operation? This seems non-obvious, > > > so a comment pointing that out would probably be helpful. > > > > The only way I could see it happening is on an arch ABI that allows > > very large pages (and has the ELF load segments aligned accordingly, > > as x86_64 does). In this case if the kernel/hardware only supported > > large (e.g. 2MB) pages, you'd pretty much always end up with >1.5MB of > > reclaimed space per DSO. IMO this is an awful kernel/hardware > > constraint to have, very wasteful, but it's exactly the situation > > where you'd most care about the gaps getting reclaimed for something > > useful. > > What I meant to ask is: apart from chunks created via reclaim_gaps, can > such oversized chunks appear as a result of malloc-family calls invoked > by the program? Yes, simple: void *p; for (i=0; i<1000; i++) p[i]=malloc(1000); for (i=0; i<1000; i++) free(p[i]); Rich
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