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a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=HAQX3MqHqmIeeOrJpELRmG+wNnU+MpmXY1sRh1DUmgw=; b=l7U4/KXYr9FFRBQAT4GXyzsgTIKNIB/DdMXvrbRRHEhxgQnNxnv7Ioku9MSbtb/xTL 1CgfNQrAKHUsd0JcdebsxN6cWJkfdQedp9bjewMRwKnlQzzF2B6GVi+SrBYAeI4ZMZvM EHQWKFyEKQbFljAXpvgT97Nq4k6+ueJLY3Yco+7da7YEcB11kL78dwusCkwg7d89/J5+ gxlu/WVUaAYGN/e/bsZeb7tQ2VANCKXatBv56L/BLne6fFz/9MSFdd8RXm3XUnYxPezb 9UsCel7XOrpyQgTYeBDkiQl1+0KE1Ctsf/+ckhFWjRZsAuQnUG1GVplO/nsHJnuE8V4h Pb+Q== X-Gm-Message-State: AFqh2kpLi9EZPYHKFwmbW1vm9wLacPFoUkjToy7uNDqILUv1q71oR1bf 0FIVCSh7HavG8TK/COcSn7LXKZxAEGAzsKBjPicGMA== X-Google-Smtp-Source: AMrXdXuGvJK/Z2GNIYTIcilU/lRPpom25Exjk2m/eTsYGxQGzPycGsZ6tbA4IcBTD/gP8jy9E/3DFgSf/xXGY41i0OE= X-Received: by 2002:a0d:f084:0:b0:4c2:51b:796c with SMTP id z126-20020a0df084000000b004c2051b796cmr993316ywe.144.1673257927353; Mon, 09 Jan 2023 01:52:07 -0800 (PST) MIME-Version: 1.0 References: <20220701142310.2188015-1-glider@google.com> <20220701142310.2188015-11-glider@google.com> <63b74a6e6a909_c81f0294a5@dwillia2-xfh.jf.intel.com.notmuch> In-Reply-To: <63b74a6e6a909_c81f0294a5@dwillia2-xfh.jf.intel.com.notmuch> From: Alexander Potapenko Date: Mon, 9 Jan 2023 10:51:30 +0100 Message-ID: Subject: Re: [PATCH v4 10/45] libnvdimm/pfn_dev: increase MAX_STRUCT_PAGE_SIZE To: Dan Williams Cc: Marco Elver , Alexander Viro , Alexei Starovoitov , Andrew Morton , Andrey Konovalov , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Christoph Hellwig , Christoph Lameter , David Rientjes , Dmitry Vyukov , Eric Dumazet , Greg Kroah-Hartman , Herbert Xu , Ilya Leoshkevich , Ingo Molnar , Jens Axboe , Joonsoo Kim , Kees Cook , Mark Rutland , Matthew Wilcox , "Michael S. Tsirkin" , Pekka Enberg , Peter Zijlstra , Petr Mladek , Steven Rostedt , Thomas Gleixner , Vasily Gorbik , Vegard Nossum , Vlastimil Babka , kasan-dev , Linux Memory Management List , Linux-Arch , LKML Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 54E0216000D X-Stat-Signature: q3wghda1g474gekm8r38663qeemgtgmy X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1673257928-426717 X-HE-Meta: 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 1rGzP26X ZTW5lwfu2u/BgEqhIow8UK9cCCqFapFAXgkmk/3F46bRlAbeZMXvyMX8bHw== 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, Jan 5, 2023 at 11:09 PM Dan Williams wro= te: > > Alexander Potapenko wrote: > > (+ Dan Williams) > > (resending with patch context included) > > > > On Mon, Jul 11, 2022 at 6:27 PM Marco Elver wrote: > > > > > > On Fri, 1 Jul 2022 at 16:23, Alexander Potapenko = wrote: > > > > > > > > KMSAN adds extra metadata fields to struct page, so it does not fit= into > > > > 64 bytes anymore. > > > > > > Does this somehow cause extra space being used in all kernel configs? > > > If not, it would be good to note this in the commit message. > > > > > I actually couldn't verify this on QEMU, because the driver never got l= oaded. > > Looks like this increases the amount of memory used by the nvdimm > > driver in all kernel configs that enable it (including those that > > don't use KMSAN), but I am not sure how much is that. > > > > Dan, do you know how bad increasing MAX_STRUCT_PAGE_SIZE can be? > > Apologies I missed this several months ago. The answer is that this > causes everyone creating PMEM namespaces on v6.1+ to lose double the > capacity of their namespace even when not using KMSAN which is too > wasteful to tolerate. So, I think "6e9f05dc66f9 libnvdimm/pfn_dev: > increase MAX_STRUCT_PAGE_SIZE" needs to be reverted and replaced with > something like: > > diff --git a/drivers/nvdimm/Kconfig b/drivers/nvdimm/Kconfig > index 79d93126453d..5693869b720b 100644 > --- a/drivers/nvdimm/Kconfig > +++ b/drivers/nvdimm/Kconfig > @@ -63,6 +63,7 @@ config NVDIMM_PFN > bool "PFN: Map persistent (device) memory" > default LIBNVDIMM > depends on ZONE_DEVICE > + depends on !KMSAN > select ND_CLAIM > help > Map persistent memory, i.e. advertise it to the memory > > > ...otherwise, what was the rationale for increasing this value? Were you > actually trying to use KMSAN for DAX pages? I was just building the kernel with nvdimm driver and KMSAN enabled. Because KMSAN adds extra data to every struct page, it immediately hit the following assert: drivers/nvdimm/pfn_devs.c:796:3: error: call to __compiletime_assert_330 declared with 'error' attribute: BUILD_BUG_ON fE BUILD_BUG_ON(sizeof(struct page) > MAX_STRUCT_PAGE_SIZE); The comment before MAX_STRUCT_PAGE_SIZE declaration says "max struct page size independent of kernel config", but maybe we can afford making it dependent on CONFIG_KMSAN (and possibly other config options that increase struct page size)? I don't mind disabling the driver under KMSAN, but having an extra ifdef to keep KMSAN support sounds reasonable, WDYT? --=20 Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Stra=C3=9Fe, 33 80636 M=C3=BCnchen Gesch=C3=A4ftsf=C3=BChrer: Paul Manicle, Liana Sebastian Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg