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Fri, 08 Nov 2024 11:25:36 -0800 (PST) Received: from [192.168.1.150] ([198.8.77.157]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-72407860a97sm4286553b3a.27.2024.11.08.11.25.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 08 Nov 2024 11:25:36 -0800 (PST) Message-ID: <07a6549a-6bbf-4e09-9e3b-128e779882a1@kernel.dk> Date: Fri, 8 Nov 2024 12:25:35 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 08/13] fs: add read support for RWF_UNCACHED To: Matthew Wilcox Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, hannes@cmpxchg.org, clm@meta.com, linux-kernel@vger.kernel.org References: <20241108174505.1214230-1-axboe@kernel.dk> <20241108174505.1214230-9-axboe@kernel.dk> Content-Language: en-US From: Jens Axboe In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: A451D1A0009 X-Stat-Signature: 5kqammrqiaqnnk1x7yinjg3pq4pcpwny X-Rspam-User: X-HE-Tag: 1731093891-955881 X-HE-Meta: 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 nRNGncqM 9Uoqm316e6jN40JwMDjNB3fjDXnbhs0xP/i0tPt7QblZvSEAG26frRlnFp+CirdHf0B8/J+BGrYLl7IlDweDSMhcwHTBNEhcaQfVNCJ4JHrcQYWnF/BR3ZvXQ6HHc0WifilPFXd4NsLHcgWdMbQiWTdVaj7vHtmUmDXoLrIjmF1jPjz+wEBKGhqALamb3fp5jf/sUgO0tzxKgcmnLhGDT+6n3vYp6ZX2sK2Mvs5rCbc0bjecKdHwKfsBziBoX4fJyQ/n8+NNHyUsD1F4blZutKnVIUjgWom3bqAT+Dk1rKenSEcM6sgSsFxcVjMBglgDiSF9KPFNILONMLcFFw8TAY85pS4clEzHnRiWHbQQc3/XGyZ++lJlsrfgi0FE2kE3h+8u6pea4x+Lj8zo7yMlO2/GaBA== 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: On 11/8/24 11:33 AM, Matthew Wilcox wrote: > On Fri, Nov 08, 2024 at 10:43:31AM -0700, Jens Axboe wrote: >> +++ b/mm/swap.c >> @@ -472,6 +472,8 @@ static void folio_inc_refs(struct folio *folio) >> */ >> void folio_mark_accessed(struct folio *folio) >> { >> + if (folio_test_uncached(folio)) >> + return; >> if (lru_gen_enabled()) { > > This feels like it might be a problem. If, eg, process A is doing > uncached IO and process B comes along and, say, mmap()s it, I think > we'll need to clear the uncached flag in order to have things work > correctly. It's a performance problem, not a correctness problem. I'll take a look, should be fine to just unconditionally clear it here. uncached is a hint after all. We'll try our best to honor it, but there will be cases where inline reclaim will fail and you'll get cached contents, particularly if you mix uncached and buffered, or uncached and mmap. -- Jens Axboe