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bh=NVZb1Kw2FmNDMOjOwuTzqSEDiuj+5VoxP2eTw4On0pE=; b=qYE1tLntalOV4p5Sdahb7kYLAh Fq2blhmozsVIHX4c2ONgkcjKdfgNAN2g9Ql7iAU6frxprhdLbQKFE6yA4pPACZVwmK15A2rUsLPSO X7Tq1Sm/KBoNtvDPfqcVOdGCUEvVMewfOhC9PQFIraoGydWNBwTuWf2DveQIK07z8DzZEUsIC7mVo +xzQjXy4kP7tXfSZuQVKbHajfby6R/79dhw5OpzYNETaUPjvo8ZsakCu+PsM6Du/HasOpFIPsvgk8 3QnZ2G9rmZrMNUT8grZl17VT4rqNWdGwtKGBziBQ8SYwweJTMJN8cEUY0dSZUy6Utj7By+dCocgH2 AVcUJaUQ==; Received: from mcgrof by bombadil.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1pVHUp-00089d-1J; Thu, 23 Feb 2023 19:43:15 +0000 Date: Thu, 23 Feb 2023 11:43:14 -0800 From: Luis Chamberlain To: Christian Brauner Cc: Christoph Hellwig , hughd@google.com, akpm@linux-foundation.org, willy@infradead.org, linux-mm@kvack.org, p.raghav@samsung.com, dave@stgolabs.net, a.manzanares@samsung.com, yosryahmed@google.com, linux-kernel@vger.kernel.org Subject: Re: [RFC v2 5/5] shmem: add support to ignore swap Message-ID: References: <20230223024412.3522465-1-mcgrof@kernel.org> <20230223024412.3522465-6-mcgrof@kernel.org> <20230223122631.hwvhbqxadvbm23nb@wittgenstein> <20230223160914.cwvt53drn2bckpdc@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230223160914.cwvt53drn2bckpdc@wittgenstein> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 98B561A0011 X-Rspam-User: X-Stat-Signature: 16f9hsigbmfqybxnt9qyypqu3kohigin X-HE-Tag: 1677181401-338467 X-HE-Meta: U2FsdGVkX18RxFMd8nbsSvNAYy8Lv5+ZuQAUWppPROFXTkSRKbBpyaD2ysKKzf7bTOW3fHflsRvUBcDOdAXNKCbOuApIofSkb33+cNI3RBYApTc5rtIyzr9+ZDrEXzsQsYvqC3TsQw1kJ407ca/h/rSZ7lZCYbNNVs+U3m7MokQ5wAwrDHtgHk0LV2HgVfufynE3jtbq4vWPMhbr+7JuPpu4Uz3XPo8S3Ts80u8V8+/JwuYnjfvW8hXRkJhjmYnKPBT26k58+XfiPs0OZ0iz2oIQNyjj+XU7ETQVob/FUf7n9OgmzB3ARhFMXpFO9U7adQAumqfq2Op20eAX8nBRsWx3LDhzzBqEMnnJvFPIXhrcbNKtMZ7Y1j+jgd6mc8381Hc9Yn4HS9Yml1Yiqqmh2TKeSBHia673niH/H/ijB05aRLugELW6khCOw8mZMVRPDauSf1OAAt5YJ7t9msfIWHulqIpPr3SfJEME4ihrxS9QZN3KCRB5IVWQu9VqXLWd7XOFENWc6NeWroXkxisxVmvY6IESQhdAJP5Ffe2ZDaLVkrziD1JOIJJxD/FCvakimFJnb4XDSc02YTZrZOEEYUgH0DOxHCH1ThbUbrQxZHKmVdjyQfvTVWd53aaFrqkH2DUi4DH7CKmISdKSkPWlJLLFY6TR4M3zatStbVijQboyMeN/Al64H/IWWXo7B9Ih5bgW0gOshq8NvBVJu1te017IbVPQSMF8ShvopHKFIP2/iuIP7a1ud1lx+8+Q3fjpDuUWOBysJQhyL9oMnfYHrh4UCAHW/M+RxRnARGxZ/mH+Ype+Q95IE77Su3fZpZnJw1kcHZEQbacjcRlLruB+ufZqSBRS8R4S8IH1DT4jVtFWfHa+I+jOXrNDl/jE2neELHqod39navL7hd8IefsnPFaWHmaLf7T3POt5w/MXY6UPjCj8OcDmq85oYkCpfyc7lYlm+fD1yZZxYjpwcQq uCyzQiAC 7eWb8FHZGi2N533Uu4frIQqZbSczLrSWvpm8AfBrejbi2H/5tDnPz1kqcvLiZmEa9saEKn3QIHBWQJqk1iLUqdDmEOVBy6sMkye/pmCmBHqH5vai4Y49j+uLo0heIywzjTZeDuUSNrr8aeDfDl3luyExSaQCdjayXIOz0dsnwCnBs2aS0diXpIPravjKKOvmielwBS7XA2geeu87iU7s24VjYVvpqpuvBT5QEbvjStgfUUFXBNBmZE/lftwkDMcOZIyxDsa2OwKvqJU8fkjZ2po+4COdevh6pY5DJg9SrCVWFifPsxf5P3mOzgS+LOoQIdv2B874X7fshQIE= 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: On Thu, Feb 23, 2023 at 05:09:14PM +0100, Christian Brauner wrote: > On Thu, Feb 23, 2023 at 07:16:09AM -0800, Christoph Hellwig wrote: > > On Thu, Feb 23, 2023 at 01:26:31PM +0100, Christian Brauner wrote: > > > We would have use-cases for this in systemd. We currently use ramfs for > > > systemd's credential logic since ramfs is unswappable. It'd be very neat > > > if we could use tmpfs instead, > > > > What is the advantage of using a swapless tmpfs over ramf? > > There are a few reasons we usually prefer tmpfs over ramfs. Iirc, ramfs > doesn't have limits and grows dynamically. So we currently only use it > from the most privileged process where we do our own accounting and > immediately remount the superblock read-only. Tmpfs on the other hand > offers various ways to restrict memory consumption. Size limits is just one bell, in fact ramfs has no configurable options. So in fact *all* options parsed on shmem_parse_options() are only available with tmpfs, some of the options are: * size * number of blocks * number of inodes * NUMA memory allocation policy * huge pages > Other reasons are that ramfs doesn't support selinux labels, xattrs, and > acls in general which come in quite handy. Starting with kernel v6.3 > tmpfs does also support idmapped mounts. So we usually always prefer > ramfs over tmpfs unless we have a very specific need such as the memory > not being swapped out. I guess its time to update Documentation/filesystems/tmpfs.rst. Luis