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[70.52.24.57]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2fe825a95c5sm92883a91.1.2025.02.25.14.30.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 25 Feb 2025 14:30:38 -0800 (PST) Message-ID: <68e82e87-606e-4443-99d3-7de6f665ce05@redhat.com> Date: Tue, 25 Feb 2025 17:30:27 -0500 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 4/4] mm: page_owner: use new iteration API To: David Hildenbrand , linux-kernel@vger.kernel.org, linux-mm@kvack.org, yuzhao@google.com, pasha.tatashin@soleen.com Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, muchun.song@linux.dev References: From: Luiz Capitulino In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: KDEJJ7rlXd9j97iHZGuSo17M6RtIJGF-c-kFcUsIZCw_1740522639 X-Mimecast-Originator: redhat.com Content-Language: en-US, en-CA Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 7C2651C000C X-Stat-Signature: m5z8jfzwh9ydp4phxbxkrw34c9p7q19u X-HE-Tag: 1740522643-48683 X-HE-Meta: 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 ESetFUJN Uybb47JxdMR/fs9l4Di0zDSgRTTg5MHCejucRqeIePOJW5NmgRzq00GW5GYBziSUVb1x6gnVeNbZQ64Stf7Sd/gA/QL4ncPUIXAMPC4D2VOlQ9N1jpeJL8cDk1LZ6zN50drnCOnMygLMK+kirMbwpOD1yiMWWKbOBpoGSYt8HYujJ3VD8MBfkmk//AtNORCct+JfBRlxMniyY8gHqCVkoRITA8hVwi8nHisIsSy0Kara7PHCwT/T0ngi4NDXys3dDG6qMFssAkBSMx0lpG98k6+hychar1Inu1HWCj74O2tEUAGCjNNSBm70w2z05QyKGc/H0tNyD4PyY5hg8WjMigQfTU30UxwM2UL/sKlEogoaHsnagDyNJqq5EDq6I1ZrZtquEJvVgupumRa1CK4cnw9QtY4DzFxRt9zOvCTQWkAORRIRMC7qXueKNAeAUEJ46hic2g8dRhSF14qccD0+P+/GUVpDVQsBKh+U4 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 2025-02-25 11:44, David Hildenbrand wrote: > On 24.02.25 22:59, Luiz Capitulino wrote: >> The page_ext_next() function assumes that page extension objects for a >> page order allocation always reside in the same memory section, which >> may not be true and could lead to crashes. Use the new page_ext >> iteration API instead. >> >> Fixes: cf54f310d0d3 ("mm/hugetlb: use __GFP_COMP for gigantic folios") >> Signed-off-by: Luiz Capitulino >> --- >>   mm/page_owner.c | 61 +++++++++++++++++++++++-------------------------- >>   1 file changed, 29 insertions(+), 32 deletions(-) >> > > [...] > >>   void __reset_page_owner(struct page *page, unsigned short order) >> @@ -293,11 +297,11 @@ void __reset_page_owner(struct page *page, unsigned short order) >>       page_owner = get_page_owner(page_ext); >>       alloc_handle = page_owner->handle; >> +    page_ext_put(page_ext); >>       handle = save_stack(GFP_NOWAIT | __GFP_NOWARN); >> -    __update_page_owner_free_handle(page_ext, handle, order, current->pid, >> +    __update_page_owner_free_handle(page, handle, order, current->pid, >>                       current->tgid, free_ts_nsec); >> -    page_ext_put(page_ext); > > I assume moving that is fine ... > > but I'll not that ... > >> -    for (i = 0; i < (1 << new_page_owner->order); i++) { >> +    rcu_read_lock(); >> +    for_each_page_ext(&old->page, 1 << new_page_owner->order, page_ext, iter) { >> +        old_page_owner = get_page_owner(page_ext); >>           old_page_owner->handle = migrate_handle; >> -        old_ext = page_ext_next(old_ext); >> -        old_page_owner = get_page_owner(old_ext); >>       } >> +    rcu_read_unlock(); >>       page_ext_put(new_ext); >>       page_ext_put(old_ext); > > ... here you are not moving it? > > > In general, LGTM, only the remaining page_ext_put() are a bit confusing. Which part you found confusing: the fact that I'm not moving them up or that we still make use of them? For this hunk, I decided to keep them where they are because 'new_page_owner', which is a page extension from 'next_ext', is still used in the last loop. So I decided to free them all at the end for simplicity. The other part is, page_ext_get() and page_ext_put() are still valid functions for getting specific page extensions outside of loops and the usage in __folio_copy_owner() (and a few other cases) seems valid to me.