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([2601:188:ca00:a00:f844:fad5:7984:7bd7]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7b1363cb3dbsm214698085a.127.2024.10.16.11.39.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Oct 2024 11:39:23 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: Date: Wed, 16 Oct 2024 14:39:22 -0400 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC 1/2] rwsem: introduce upgrade_read interface To: Matthew Wilcox , Waiman Long Cc: lizhe.67@bytedance.com, peterz@infradead.org, mingo@redhat.com, will@kernel.org, boqun.feng@gmail.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20241016043600.35139-1-lizhe.67@bytedance.com> <20241016043600.35139-2-lizhe.67@bytedance.com> <7f7b277a-7019-4bf4-b100-0505c6ce9737@redhat.com> In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/alternative; boundary="------------FQP6uoHMLRh2d6njkcZL8j35" Content-Language: en-US X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: A798B4000E X-Stat-Signature: ukry5kks5y47xskar4becq3cis1zcayt X-Rspam-User: X-HE-Tag: 1729103960-40608 X-HE-Meta: U2FsdGVkX19lNLpVyLI7+C3LzvCP0VPiCiqOYss1c1WXs2zZqMwxBsPJGuH4ybNnqj6W9DuwxTLVVKzgimdr9VkNzwwwsGOe9AWUFtKRslcaboI43ixMz1p8+RQDF48IWG4FAj7+PmrOiI72iFO+/6MmykT5A0kIKlVsh6h6GvXiOUlVjj/AKXrTBkJGLuwNx9F6cTvX/CxEn/KKPI6z0MGZiiuAWs3Py51W9Utr+RysAAzZ/kJYAbZG0FESh2o4l9x2i8QrtgfeaQUWGWdA70WQ2s73DHAZpZjOpZjHCbZPEKMeUUWDR+YMWjfpBalKgN2AcmtFcMxvBcpT+fYUH9U32b7E+TpDCzvLmzkzCxMWdhOjoTfTvewzNfgTl/WwKf/Fk8LkC6vo7+L2K64o8c0wN5o4S2hzK7K5KgZ7oU1y19Q4ca9GFkaoTUwp4gO8E3YwyAEiZZDb9n306ZAHEaCMsRzam6RxzT9v9xBx8jxob11KmWbpgqbNbhX2MbAeOtmtx1vgb05Pe0oeUwwFR31jGJlPG0z5I49Ijcw6aMxCJZOpSZtMuD6DU4/8OJyEV2JQP5uJqVGIGiQxf66m0b3TvZykfYcfd8TYkKilgqQ1dEQ2ecl7cRONaT4fbOGb1yMwOmw2E25/5HzIkNnquKiyvzXjrwMQUYVlj5isFSmW3tmCr3eoDy0mxYzGVS0rLrja/fd2eDu/Bq8ZocQqUxEkCcC2afNBHbA8b/qQxZ4a5cVifrroe2wJNO+6yfge8zeCRl1Ve+ZgEwjrDg5+dkrsYCn1ToK9ruIZREIQXhMbgMy2vNdMZ2m/ChEI+eeQhfbHXRzwNoSLR3t8Af5Fz4gfHodwhEKAOAZjigigHtF5Ze9E9j6AS1QpjjMWyHQrIk1oZeDWEI4ZaKX7UwwL7w7xedUcPy01tYPs+FYPcAs/ozz2rrg0VjogRgOgtLXj3Se161TEk/IvyLlFFG2 7HZEbp/B 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000594, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: This is a multi-part message in MIME format. --------------FQP6uoHMLRh2d6njkcZL8j35 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 10/16/24 2:05 PM, Matthew Wilcox wrote: > On Wed, Oct 16, 2024 at 10:23:14AM -0400, Waiman Long wrote: >> Another alternative that I have been thinking about is a down_read() variant >> with intention to upgrade later. This will ensure that only one active >> reader is allowed to upgrade later. With this, upgrade_read() will always >> succeed, maybe with some sleeping, as long as the correct down_read() is >> used. > How is that different from Kent's SIX locks other than you can take an > rwsem for write immediately (SIX locks have to be taken for Intent and > then Upgraded)? Yes, it is modeled after Kent's SIX locks. The goal is to eventually eliminate the need of a separate SIX lock. Cheers, Longman --------------FQP6uoHMLRh2d6njkcZL8j35 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: 7bit
On 10/16/24 2:05 PM, Matthew Wilcox wrote:
On Wed, Oct 16, 2024 at 10:23:14AM -0400, Waiman Long wrote:

Another alternative that I have been thinking about is a down_read() variant
with intention to upgrade later. This will ensure that only one active
reader is allowed to upgrade later. With this, upgrade_read() will always
succeed, maybe with some sleeping, as long as the correct down_read() is
used.

How is that different from Kent's SIX locks other than you can take an
rwsem for write immediately (SIX locks have to be taken for Intent and
then Upgraded)?

Yes, it is modeled after Kent's SIX locks. The goal is to eventually eliminate the need of a separate SIX lock.

Cheers,
Longman

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