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Re: [PATCH v2] Allow shrinking of arena heaps using mmap based onovercommit settings when available

From: Siddhesh Poyarekar <siddhesh at redhat dot com>
To: Roland McGrath <roland at hack dot frob dot com>
Cc: KOSAKI Motohiro <kosaki dot motohiro at gmail dot com>, "Carlos O'Donell"<carlos at systemhalted dot org>, Rich Felker <dalias at aerifal dot cx>, libc-alpha at sourceware dot org
Date: Fri, 24 Aug 2012 08:37:38 +0530
Subject: Re: [PATCH v2] Allow shrinking of arena heaps using mmap based onovercommit settings when available
References: <20120720223800.GB26330@sunsite.ms.mff.cuni.cz><20120720224417.E8BEF2C0CA@topped-with-meat.com><20120721061814.GC26330@sunsite.ms.mff.cuni.cz><20120721133217.GY544@brightrain.aerifal.cx><20120725183634.E0C5F2C0B1@topped-with-meat.com><CAHGf_=qCMy6K1MD4miN65GkMSumYTtH23xoFrfmCuh=WjybAVA@mail.gmail.com><20120730230006.355f9b67@spoyarek><5016D012.5000101@gmail.com><20120730191758.GX544@brightrain.aerifal.cx><CAHGf_=rRm4B4YCZKgos5hWN_QTYV76fAxcegO7D3x=4_A88Rvw@mail.gmail.com><20120731132705.GZ544@brightrain.aerifal.cx><CAHGf_=pN3KJGL_V1tQ2+o0=-RY4q2du7PJDnak9y7xyzYiH1tQ@mail.gmail.com><20120810235226.408e3cec@spoyarek><CADZpyiz05WnMqrREEtSs+oW_0Ld6hnfxbmFMk_hKYL-P_gFTag@mail.gmail.com><20120811205228.42ab905f@spoyarek><CADZpyizkMLBGK13-h-YH_CpVgbcx3n7gbxYAwxzsdbiEJOMNjg@mail.gmail.com><50289F84.9060205@gmail.com><20120822000610.6110da3f@spoyarek><20120822141946.7702d182@spoyarek><20120823205321.A03E02C0FB@topped-with-meat.com>

On Thu, 23 Aug 2012 13:53:21 -0700 (PDT), Roland wrote:
> > +  static int may_shrink_heap = -1;
> > +
> > +  if (__builtin_expect (may_shrink_heap < 0, 0))
> > +    may_shrink_heap = check_may_shrink_heap ();
> 
> Just call check_may_shrink_heap () directly in the use below.
> Leave it to the malloc-sysdep.h inline to cache or whatnot.
> 

That would lead to /proc/sys/vm/overcommit_memory being opened and
closed with every call to shrink heap on Linux. The general case would
be fine. Do we really want that?

Regards,
Siddhesh

Follow-Ups:
- Re: [PATCH v2] Allow shrinking of arena heaps using mmap based onovercommit settings when available
  - From: Rich Felker

References:
- Re: [PATCH][RFC] Allow explicit shrinking of arena heaps using anenvironment variable
  - From: KOSAKI Motohiro
- Re: [PATCH][RFC] Allow explicit shrinking of arena heaps using anenvironment variable
  - From: Siddhesh Poyarekar
- Re: [PATCH][RFC] Allow explicit shrinking of arena heaps using anenvironment variable
  - From: Carlos O'Donell
- Re: [PATCH][RFC] Allow explicit shrinking of arena heaps using anenvironment variable
  - From: Siddhesh Poyarekar
- Re: [PATCH][RFC] Allow explicit shrinking of arena heaps using anenvironment variable
  - From: Carlos O'Donell
- Re: [PATCH][RFC] Allow explicit shrinking of arena heaps using anenvironment variable
  - From: KOSAKI Motohiro
- [PATCH v2] Allow shrinking of arena heaps using mmap based onovercommit settings when available
  - From: Siddhesh Poyarekar
- Re: [PATCH v2] Allow shrinking of arena heaps using mmap based onovercommit settings when available
  - From: Siddhesh Poyarekar
- Re: [PATCH v2] Allow shrinking of arena heaps using mmap based onovercommit settings when available
  - From: Roland McGrath

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