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(p200300d82f434700d2cd2b81d4e68b2a.dip0.t-ipconnect.de. [2003:d8:2f43:4700:d2cd:2b81:d4e6:8b2a]) by smtp.gmail.com with ESMTPSA id e22-20020a05600c219600b003fbfea1afffsm2625209wme.27.2023.07.27.14.10.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 27 Jul 2023 14:10:55 -0700 (PDT) Message-ID: <57c10b7b-c577-d92d-cdd8-37b535c63931@redhat.com> Date: Thu, 27 Jul 2023 23:10:55 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH] mm: Improve the comment in isolate_migratepages_block() To: Matthew Wilcox , Andrew Morton Cc: linux-mm@kvack.org, "Kirill A. Shutemov" References: From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 625D01C0005 X-Stat-Signature: dofr7b8jf5m5jim3qc7xihyx4phfwukg X-HE-Tag: 1690492260-877317 X-HE-Meta: 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 efS0JUVJ 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 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 27.07.23 22:39, Matthew Wilcox wrote: > A recent patch shows that not everybody understands that "stabilise the > mapping" really means "prevent the mapping from being freed", so change > the wording to hopefully make that more clear. > > Signed-off-by: Matthew Wilcox (Oracle) > > diff --git a/mm/compaction.c b/mm/compaction.c > index 9641e2131901..9be2c3504ff2 100644 > --- a/mm/compaction.c > +++ b/mm/compaction.c > @@ -1095,13 +1095,13 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn, > bool migrate_dirty; > > /* > - * Only pages without mappings or that have a > - * ->migrate_folio callback are possible to migrate > - * without blocking. However, we can be racing with > - * truncation so it's necessary to lock the page > - * to stabilise the mapping as truncation holds > - * the page lock until after the page is removed > - * from the page cache. > + * Only folios without mappings or that have > + * a ->migrate_folio callback are possible to > + * migrate without blocking. However, we may > + * be racing with truncation, which can free > + * the mapping. Truncation holds the folio lock > + * until after the folio is removed from the page > + * cache so holding it ourselves is sufficient. > */ > if (!folio_trylock(folio)) > goto isolate_fail_put; > Reviewed-by: David Hildenbrand -- Cheers, David / dhildenb