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Tue, 10 Dec 2024 11:01:27 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id rKrhG4cfWGfnUAAAD6G6ig (envelope-from ); Tue, 10 Dec 2024 11:01:27 +0000 Message-ID: <1791a2ad-30c6-47db-914f-cfcc359e04b2@suse.cz> Date: Tue, 10 Dec 2024 12:01:27 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 5/6] mm/slab: allow freeptr_offset to be used with ctor Content-Language: en-US To: Suren Baghdasaryan , akpm@linux-foundation.org Cc: willy@infradead.org, liam.howlett@oracle.com, lorenzo.stoakes@oracle.com, mhocko@suse.com, hannes@cmpxchg.org, mjguzik@gmail.com, oliver.sang@intel.com, mgorman@techsingularity.net, david@redhat.com, peterx@redhat.com, oleg@redhat.com, dave@stgolabs.net, paulmck@kernel.org, brauner@kernel.org, dhowells@redhat.com, hdanton@sina.com, hughd@google.com, minchan@google.com, jannh@google.com, shakeel.butt@linux.dev, souravpanda@google.com, pasha.tatashin@soleen.com, corbet@lwn.net, linux-doc@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com References: <20241206225204.4008261-1-surenb@google.com> <20241206225204.4008261-6-surenb@google.com> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Queue-Id: ECA802001B X-Stat-Signature: 1odrc5kbr76pfk7zoe5eq39r6shid9qo X-Rspam-User: X-Rspamd-Server: rspam11 X-HE-Tag: 1733828480-89656 X-HE-Meta: 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 07KvUZa5 o9DHgU9Zma+iPVocRtLI93WoAfBcozZC/CxtA3//uaoZSxOmphAQvpvkdcMpnnb4POtI7jzOqwOrNzwehtuEi6HVBBiQzw9JsLaYN+TPSSjIFef/3pfU/1TpY042QKO9A1iqAfOY8M/Vz/dBiFv5y5hAoNe37qSX/1fyahh5rZb768wtD/HlkDWUJdyxbcV7nbcWGPPcZAZtZO/KY80t0Vpqb7G7z+CXiawyS1FyeNDaae7FbVogHM7WbICfm4lvERafzh3xAp7/b85AizQs113Ki5EUjL9X1f9v0xiJrg2AVlnaek0AzXt+YdvkU+zOpbZP1vLa+hiDw0h56jNcRNd3chBvtxnop4urhXD6k2nLfEdHxQrRtVQDsnQs4uV1H1MKeWfZvFc/fcXI= 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 12/6/24 23:52, Suren Baghdasaryan wrote: > There is no real reason to prevent freeptr_offset usage when a slab > cache has a ctor. The only real limitation is that any field unioned > with the free pointer and initialized by ctor will be overwritten since > free pointer is set after @ctor invocation. Document this limitation > and enable usage of freeptr_offset with ctor. > > Suggested-by: Vlastimil Babka > Signed-off-by: Suren Baghdasaryan Reviewed-by: Vlastimil Babka > --- > include/linux/slab.h | 5 +++-- > mm/slub.c | 2 +- > 2 files changed, 4 insertions(+), 3 deletions(-) > > diff --git a/include/linux/slab.h b/include/linux/slab.h > index 681b685b6c4e..6bad744bef5e 100644 > --- a/include/linux/slab.h > +++ b/include/linux/slab.h > @@ -305,8 +305,9 @@ struct kmem_cache_args { > * Using %0 as a value for @freeptr_offset is valid. If @freeptr_offset > * is specified, %use_freeptr_offset must be set %true. > * > - * Note that @ctor currently isn't supported with custom free pointers > - * as a @ctor requires an external free pointer. > + * Note that fields unioned with free pointer cannot be initialized by > + * @ctor since free pointer is set after @ctor invocation, so those > + * values will be overwritten. > */ > unsigned int freeptr_offset; > /** > diff --git a/mm/slub.c b/mm/slub.c > index 870a1d95521d..f62c829b7b6b 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5462,7 +5462,7 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s) > s->inuse = size; > > if (((flags & SLAB_TYPESAFE_BY_RCU) && !args->use_freeptr_offset) || > - (flags & SLAB_POISON) || s->ctor || > + (flags & SLAB_POISON) || (s->ctor && !args->use_freeptr_offset) || > ((flags & SLAB_RED_ZONE) && > (s->object_size < sizeof(void *) || slub_debug_orig_size(s)))) { > /*