Received-SPF: pass (google.com: domain of linux-kernel+bounces-47580-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Message-ID: <08a4971e-c31d-46f7-afbc-7404bd9a293f@arm.com>
Date: Thu, 1 Feb 2024 09:00:23 +0530
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH RFC v3 12/35] mm: Call arch_swap_prepare_to_restore()
 before arch_swap_restore()
Content-Language: en-US
To: Alexandru Elisei <alexandru.elisei@arm.com>, 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
Cc: pcc@google.com, steven.price@arm.com, vincenzo.frascino@arm.com,
 david@redhat.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
References: <20240125164256.4147-1-alexandru.elisei@arm.com>
 <20240125164256.4147-13-alexandru.elisei@arm.com>
From: Anshuman Khandual <anshuman.khandual@arm.com>
In-Reply-To: <20240125164256.4147-13-alexandru.elisei@arm.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit


On 1/25/24 22:12, Alexandru Elisei wrote:
> arm64 uses arch_swap_restore() to restore saved tags before the page is
> swapped in and it's called in atomic context (with the ptl lock held).
> 
> Introduce arch_swap_prepare_to_restore() that will allow an architecture to
> perform extra work during swap in and outside of a critical section.
> This will be used by arm64 to allocate a buffer in memory where to
> temporarily save tags if tag storage is not available for the page being
> swapped in.

Just wondering if tag storage will always be unavailable for tagged pages
being swapped in ? OR there are cases where allocation might not even be
required ? This prepare phase needs to be outside the critical section -
only because there might be memory allocations ?