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[178.5.232.220]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-aa5998e6fa4sm512456966b.116.2024.12.02.07.04.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 02 Dec 2024 07:04:27 -0800 (PST) Date: Mon, 2 Dec 2024 16:04:24 +0100 From: Dmitry Dolgov <9erthalion6@gmail.com> To: David Hildenbrand Cc: linux-mm@kvack.org Subject: Re: [QUESTION] Resizing shared mapping without clashing with others Message-ID: References: <3kpxpd3dbjgg6epasi2554c4qyils4t3cm2pjnyzer7gkyoaxl@khhdxjiggyhp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: gnf3farrds97gzfdztrk8rfid7d9x1uu X-Rspam-User: X-Rspamd-Queue-Id: 914808003A X-Rspamd-Server: rspam08 X-HE-Tag: 1733151847-930515 X-HE-Meta: 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 abBZG6VF e+tjCs+k2NmO8o976v2R+P/0qGUa1ZKio+8I/yAp9ftVDOrDDq6S1sztyYQ4Lp3Q9eQg3P2myRtMz+MW2vNPxeVMjaxkhFcE9gabdGYdK2N1sVP6sZ1gU25KIRXw580p+zWYQ1aSoy9lxD4anzkQuTboe7Byjg/sqA4QLmIDlwPR+d5Won3F4euFcwTb3AN8akY8m8T3cpZA2+A71qD9q/LNCrDlK33fCV9vZCZloRkqTldkUtzmMBGGewRxL36liAPSZEd3tx742t0VV4CGuCVJoN4eB6ExQVXPxuUMCXoNRcqI7oLMCdCD7DEwGwK/+BSY4om3+Ldj5GVeR6TOFpgb3ormoqqU5luu0aLWWxzAT0zyUIuKI38v52RnVPp2wgfafUs5h45JA6Zg= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000037, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On Mon, Dec 02, 2024 at 12:07:01PM GMT, David Hildenbrand wrote: > > Likely it's best to look into reserving a large VMA space using > mmap(MAP_PRIVATE|MA_ANON, PROT_NONE); it's reserved but inaccessible, so it > cannot get reallocated for different purposes. Then converting pieces of > that into actually usable shared anonymous memory (e.g., MAP_FIXED). Yes, we've considered this option, preparing an initial "reserving" mapping, then take pieces out of it for usage. As I've mentioned to Matthew, there seems to be arguments against this approach. In a few words: * The impact on OOM decisions is not clear (at least to me). * In certain cases this will be counted against a reservation limits, although we don't use the memory yet (e.g. with hugetlb insige a cgroup with hugetlb.2MB.rsvd.limit_in_bytes set).