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([2001:a61:2553:a401:cfc6:2039:a9ec:21ff]) by smtp.gmail.com with ESMTPSA id s9sm8657094edd.16.2021.04.04.12.28.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 04 Apr 2021 12:29:00 -0700 (PDT) Cc: mtk.manpages@gmail.com, linux-mm@kvack.org Subject: Re: [patch] Clarify that MAP_POPULATE is best-effort To: Bruce Merry , linux-man@vger.kernel.org, Alejandro Colomar References: <20210323074831.GA7535@kryton.kat.ac.za> From: "Michael Kerrisk (man-pages)" Message-ID: <36f6ac8a-e746-5546-5354-35b86dcff4ca@gmail.com> Date: Sun, 4 Apr 2021 21:28:57 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: <20210323074831.GA7535@kryton.kat.ac.za> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: DC57AE0001AC X-Stat-Signature: 7sw7kwrbubj6ekpdjakwcfgyho9qp9ai X-Rspamd-Server: rspam02 Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf30; identity=mailfrom; envelope-from=""; helo=mail-ej1-f41.google.com; client-ip=209.85.218.41 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617564538-138276 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hello Bruce, On 3/23/21 8:48 AM, Bruce Merry wrote: > As discussed on linux-mm > (https://marc.info/?l=linux-mm&m=161528594100612&w=2), MAP_POPULATE can > fail silently if the hugetlb cgroup settings allow huge page reservation > but prevents huge pages being allocated. > > Closes https://bugzilla.kernel.org/show_bug.cgi?id=212153. > --- > man2/mmap.2 | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/man2/mmap.2 b/man2/mmap.2 > index 164ba196e..03f2eeb2c 100644 > --- a/man2/mmap.2 > +++ b/man2/mmap.2 > @@ -400,6 +400,11 @@ private writable mappings. > Populate (prefault) page tables for a mapping. > For a file mapping, this causes read-ahead on the file. > This will help to reduce blocking on page faults later. > +The > +.BR mmap () > +call doesn't fail if the mapping cannot be populated (for example, due > +to limitations on the number of mapped huge pages when using > +.BR MAP_HUGETLB ). > .BR MAP_POPULATE > is supported for private mappings only since Linux 2.6.23. > .TP Thanks. Patch applied. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/