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Thu, 27 Feb 2025 12:51:09 -0800 (PST) X-Google-Smtp-Source: AGHT+IFXSchHq2foaKrZLcs7V3jjAhGMmCw06E/p0SekC5qwicuW3MsABzATaaIO/h6J8cBe2E3BBA== X-Received: by 2002:a05:622a:6001:b0:474:bc8b:3f3d with SMTP id d75a77b69052e-474bc8b3fe6mr1682121cf.7.1740689469558; Thu, 27 Feb 2025 12:51:09 -0800 (PST) Received: from [192.168.2.110] ([70.52.24.57]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-474691a11fdsm15260961cf.15.2025.02.27.12.51.08 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 27 Feb 2025 12:51:09 -0800 (PST) Message-ID: <7ca09134-271e-48aa-b965-14fddd0504d9@redhat.com> Date: Thu, 27 Feb 2025 15:50:58 -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: <68e82e87-606e-4443-99d3-7de6f665ce05@redhat.com> <5bb20271-a92a-454e-90e7-8812fd01d31d@redhat.com> From: Luiz Capitulino In-Reply-To: <5bb20271-a92a-454e-90e7-8812fd01d31d@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: w3mpBg3fk5da6G2x64wPIsRtt-e0tYPuw7cbSRSZ_TY_1740689470 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-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 44BF6A0016 X-Rspam-User: X-Stat-Signature: r988kb881jtzpkh7zmx8s7xwq8o8jo69 X-HE-Tag: 1740689474-922653 X-HE-Meta: U2FsdGVkX18fJ8CfMtc8MPLdVATy9YSo+JwExGMzd/03tquBpvkDY79IC8ZajBl78/TyXeu3HPtu8sDcWq5RzUVXbbn7N5/pSI0I3+VaMfz6n3h9th2EEe6CiFrt81Mw9XG6kku9oY+ylmSskU3JPG0ZgUJnvfapAoN3HoRhgzr/IF1iNFtV3YSMEHVFd2kYBZBx4vQZKkS+78eRzO1+S1ftT3le0tnhNuoMmMujo9sU5cccE2n75vIpRQRMvVFWpupIi5QTcpMIRxYqXt8WQje3fZ2c0j3CfJfvaD6Rr4FnueylVedMu5jKHrkONgLf2/nFJ7GI+v90g+z8xBenugM99gDpuZoyBfXXIXmUQ7Jsy6p0QZqVdgLqKdS/lODmPaAMVL9uTMqme/8cTe+ZQvYGnxpWMS7WyRIV8akFl3GjuEtPh0SCfMONVqPBhZxNIQaUIO0cBydMwKxgC7vvOiRTncZpc1yJhnKqcnCuDHul2LItaPDvs+fGF0tlPY0UcdWqOfP6CkC0j3hB61N5XkE4iMBSBx49bFbxNg77LGeijQkqpV1V00XXxYu7DKn4f7ahtjniQGe+yKnUL1tmzHN5IhoFHgp8k9eHUYboW0MNpVkgJcgdtPgD0uvdYXiSzvud0A9vXCuAZokk9/Oy+fEHE3lE4rt/o65bFIS5KEapEO24eaHMyaLwM2RFFdeAljtD9l8Y72mEeVA9y+eL3ww/lpVwHxGGTmE0bkVXlSYs/7dh1MnuGIImDNd9OISTPYTh+ncTyAHZlOHhU+/sBYwlMUbixURf/CQZY9BzpJ+De0CA8M4c+wQU9mkNdQAno4OGIzFGEHp0RepJuuJ8BmbzlrUyGB1NaiQu7ddKwFN/YEmnJlk75Tz12hvr4HJCqj8sUdQRKTwEPy2jaUOO855aj1pW5Y8HY7eVkUskFK2yX9/F/aafRiJKQAQOQiSDtjaEXo5bohiA0aB2Is0 9nHxavN9 Rmw53p1XUD/1TeA37ZrolXkGgZNTfEmGVfj5pJJiUh01V/bg+UejvCGTvpqOtRlGpBCTwEWqZGj+7edHAx2DmQQJxR+zjdlt0VrJUjjRnMLrBEjv2bMbjAfHTng7aopRRPDStcrqZ1xwXcMLm9MC6Tdg7Yu0641mREZQJXDtK82d5RZ2hqRUM/PWD5UHQG3ycUbwREZA3D4f2Z9nQjyZMvt+D7KXhr0mZ+5zyo/P74x9MAq3xXxYhOBHCOWoMsSwD3buRimuy5VLIFU6pPWot4D5f5l2tSWwURRO3FvE//UQ2m5sBLMBzTH2xNduA42Ha0go0BX0NSvP0XA/I1icDCWSG7Ch7eVavKekb8I6L1jp85yaT++YtBaCvs1Kijc3VYgaWCTJUdPY+GuvpDP3BJWx1FibaiLJP2Gnj8tYw5VHsiDYEePiLWtkPjkl9TtfdOOgKJuZOJGOQ1VO/yiBmffIWP4Mlsv7wLp9D 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 2025-02-27 08:50, David Hildenbrand wrote: > On 25.02.25 23:30, Luiz Capitulino wrote: >> 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? > > How we are deferring page_ext_put() when not actually working on these > values anymore. The page_owner itself should not go away here unless we > have a serious bug. > > To be precise, can't we simply do the following on top? Yes, that looks good and I like how the new API allows for simpler code. My only concern is that if the user is not familiar with the page_ext internals, it might not be clear what page_ext_put() is actually protecting in which case it looks wrong that we're using a reference returned by get_page_owner() after releasing the lock. If you think that that's not an issue then I can apply this change on top. > > diff --git a/mm/page_owner.c b/mm/page_owner.c > index c9d2c688eb981..12044340adf89 100644 > --- a/mm/page_owner.c > +++ b/mm/page_owner.c > @@ -356,26 +356,24 @@ void __split_page_owner(struct page *page, int old_order, int new_order) > >  void __folio_copy_owner(struct folio *newfolio, struct folio *old) >  { > -       struct page_ext *old_ext; > -       struct page_ext *new_ext; >         struct page_ext *page_ext; >         struct page_ext_iter iter; >         struct page_owner *old_page_owner; >         struct page_owner *new_page_owner; >         depot_stack_handle_t migrate_handle; > > -       old_ext = page_ext_get(&old->page); > -       if (unlikely(!old_ext)) > +       page_ext = page_ext_get(&old->page); > +       if (unlikely(!page_ext)) >                 return; > +       old_page_owner = get_page_owner(page_ext); > +       page_ext_put(page_ext); > > -       new_ext = page_ext_get(&newfolio->page); > -       if (unlikely(!new_ext)) { > -               page_ext_put(old_ext); > +       page_ext = page_ext_get(&newfolio->page); > +       if (unlikely(!page_ext)) >                 return; > -       } > +       new_page_owner = get_page_owner(page_ext); > +       page_ext_put(page_ext); > > -       old_page_owner = get_page_owner(old_ext); > -       new_page_owner = get_page_owner(new_ext); >         migrate_handle = new_page_owner->handle; >         __update_page_owner_handle(&newfolio->page, old_page_owner->handle, >                                    old_page_owner->order, old_page_owner->gfp_mask, > @@ -402,9 +400,6 @@ void __folio_copy_owner(struct folio *newfolio, struct folio *old) >                 old_page_owner->handle = migrate_handle; >         } >         rcu_read_unlock(); > - > -       page_ext_put(new_ext); > -       page_ext_put(old_ext); >  } > >  void pagetypeinfo_showmixedcount_print(struct seq_file *m, > >