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[70.27.3.10]) by smtp.gmail.com with ESMTPSA id w2-20020a05622a134200b0034454d0c8f3sm11036763qtk.93.2022.09.01.09.28.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Sep 2022 09:28:58 -0700 (PDT) Date: Thu, 1 Sep 2022 12:28:57 -0400 From: Peter Xu To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, "Kirill A . Shutemov" , Sasha Levin , "Aneesh Kumar K . V" , Vlastimil Babka , Jerome Marchand , Andrea Arcangeli , Hugh Dickins , Jason Gunthorpe , John Hubbard , Yang Shi Subject: Re: [PATCH v1] mm/gup: adjust stale comment for RCU GUP-fast Message-ID: References: <20220901072119.37588-1-david@redhat.com> MIME-Version: 1.0 In-Reply-To: <20220901072119.37588-1-david@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1662049743; a=rsa-sha256; cv=none; b=Cy/m0jWQs/Rcs3mahnidnFstB9eGRH2JavPbVxIbfnBFQmdA2d6FoZ1BXH3HvckrAkZTek 4IWnTjbJe1Ca3fj73oGoynhLPSqBZfklyn7uP1Y2wPJrrXhpttF45ku99zMAldhTk7CopE sS69N3yyPdzjmAestR1xm3oCTUB0mnM= ARC-Authentication-Results: i=1; imf28.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=S71z7eKW; spf=pass (imf28.hostedemail.com: domain of peterx@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1662049743; 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:dkim-signature; bh=Ss+788P3BPmasfJtALEqRKNF7dmBsC3V1B9rlxVbN7E=; b=JQLvLaBNqmyyQDL3kbOPBq0D3TM9gkNiDekcUWQR2eDZwTbudV7iLctgq2pIjA+kbtDN9U ggwj78Ls39Syk7gJa7qIggyn6d/rxB7LYqgGEIXtToMN5X4ekSep8jeoFaEZ0Kl1dL1KyJ qB3QT3os5fqWw1U/P8IREP+NWtkzNS4= X-Stat-Signature: s8wdxy8y6ob5z6j7wy3bqnio5zpmjy56 X-Rspam-User: X-Rspamd-Queue-Id: A8ECCC006E X-Rspamd-Server: rspam07 Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=S71z7eKW; spf=pass (imf28.hostedemail.com: domain of peterx@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=peterx@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-HE-Tag: 1662049743-511715 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, Sep 01, 2022 at 09:21:19AM +0200, David Hildenbrand wrote: > commit 4b471e8898c3 ("mm, thp: remove infrastructure for handling splitting > PMDs") didn't remove all details about the THP split requirements for > RCU GUP-fast. > > IPI broeadcasts on THP split are no longer required. > > Cc: Kirill A. Shutemov > Cc: Sasha Levin > Cc: Aneesh Kumar K.V > Cc: Vlastimil Babka > Cc: Jerome Marchand > Cc: Andrea Arcangeli > Cc: Hugh Dickins > Cc: Jason Gunthorpe > Cc: John Hubbard > Cc: Peter Xu > Cc: Yang Shi > Signed-off-by: David Hildenbrand > --- > mm/gup.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index 5abdaf487460..cfe71f422787 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2309,9 +2309,8 @@ EXPORT_SYMBOL(get_user_pages_unlocked); > * > * Another way to achieve this is to batch up page table containing pages > * belonging to more than one mm_user, then rcu_sched a callback to free those > - * pages. Disabling interrupts will allow the fast_gup walker to both block > - * the rcu_sched callback, and an IPI that we broadcast for splitting THPs > - * (which is a relatively rare event). The code below adopts this strategy. > + * pages. Disabling interrupts will allow the fast_gup walker to block the > + * rcu_sched callback. This is the comment for fast-gup in general but not only for thp split. I can understand that we don't need IPI for thp split, but isn't the IPIs still needed for thp collapse (aka pmdp_collapse_flush)? -- Peter Xu