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a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1701191854; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=BDp4qsyVqR2xMh/m4hIcHNoVew/4DfGfZNkEPyCM7Bo=; b=jTw7NKIdzXjh1muMGqipUhBkAusOrWyiFntsj9///YcIRIf/L/tPqaeViuIrl1LRmL1fuo aZ2kgQgLle8ShGEBINI7Uf11mEzkBcZi7nfeVvWBwfqRJXcpiSHmY7vM3nY6nCQt4WHBGS JknDS0sqxoESUcz2+1yMD9kHNnD8k60= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 99F93C15; Tue, 28 Nov 2023 09:18:20 -0800 (PST) Received: from raptor (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3F3773F6C4; Tue, 28 Nov 2023 09:17:28 -0800 (PST) Date: Tue, 28 Nov 2023 17:17:25 +0000 From: Alexandru Elisei To: David Hildenbrand Cc: catalin.marinas@arm.com, will@kernel.org, oliver.upton@linux.dev, maz@kernel.org, james.morse@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, arnd@arndb.de, akpm@linux-foundation.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, mhiramat@kernel.org, rppt@kernel.org, hughd@google.com, pcc@google.com, steven.price@arm.com, anshuman.khandual@arm.com, vincenzo.frascino@arm.com, eugenis@google.com, kcc@google.com, hyesoo.yu@samsung.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH RFC v2 05/27] mm: page_alloc: Add an arch hook to allow prep_new_page() to fail Message-ID: References: <20231119165721.9849-1-alexandru.elisei@arm.com> <20231119165721.9849-6-alexandru.elisei@arm.com> <0a0f9345-3138-4e89-80cd-c7edaf2ff62d@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0a0f9345-3138-4e89-80cd-c7edaf2ff62d@redhat.com> X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 73F6D1A002F X-Stat-Signature: co571tjinsfkensi8wk399gcej8odi36 X-HE-Tag: 1701191854-806053 X-HE-Meta: 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 OjjIz3aZ VsTOy2PlcY7maVjbjZlXbC9ROksxM/+xUZocfmq6d8NNwqKORmudIm3aWDQDiXHOXzoxcqEwNowg6l7vbVexgoRJAndEmPhIEreYgGt5u+hUMBZK+tgaxhXmem0Ya6IpcQ5t1MpFQW2mP8J02peYwD245CuZg/OtJdOeJ 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: List-Subscribe: List-Unsubscribe: Hi, On Tue, Nov 28, 2023 at 05:57:31PM +0100, David Hildenbrand wrote: > On 27.11.23 13:09, Alexandru Elisei wrote: > > Hi, > > > > Thank you so much for your comments, there are genuinely useful. > > > > On Fri, Nov 24, 2023 at 08:35:47PM +0100, David Hildenbrand wrote: > > > On 19.11.23 17:56, Alexandru Elisei wrote: > > > > Introduce arch_prep_new_page(), which will be used by arm64 to reserve tag > > > > storage for an allocated page. Reserving tag storage can fail, for example, > > > > if the tag storage page has a short pin on it, so allow prep_new_page() -> > > > > arch_prep_new_page() to similarly fail. > > > > > > But what are the side-effects of this? How does the calling code recover? > > > > > > E.g., what if we need to populate a page into user space, but that > > > particular page we allocated fails to be prepared? So we inject a signal > > > into that poor process? > > > > When the page fails to be prepared, it is put back to the tail of the > > freelist with __free_one_page(.., FPI_TO_TAIL). If all the allocation paths > > are exhausted and no page has been found for which tag storage has been > > reserved, then that's treated like an OOM situation. > > > > I have been thinking about this, and I think I can simplify the code by > > making tag reservation a best effort approach. The page can be allocated > > even if reserving tag storage fails, but the page is marked as invalid in > > set_pte_at() (PAGE_NONE + an extra bit to tell arm64 that it needs tag > > storage) and next time it is accessed, arm64 will reserve tag storage in > > the fault handling code (the mechanism for that is implemented in patch #19 > > of the series, "mm: mprotect: Introduce PAGE_FAULT_ON_ACCESS for > > mprotect(PROT_MTE)"). > > > > With this new approach, prep_new_page() stays the way it is, and no further > > changes are required for the page allocator, as there are already arch > > callbacks that can be used for that, for example tag_clear_highpage() and > > arch_alloc_page(). The downside is extra page faults, which might impact > > performance. > > > > What do you think? > > That sounds a lot more robust, compared to intermittent failures to allocate > pages. Great, thank you for the feedback, I will use this approach for the next iteration of the series. Thanks, Alex > > -- > Cheers, > > David / dhildenb >