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Tue, 27 Aug 2024 21:10:11 +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 eJ5jBLNAzmaNDgAAD6G6ig (envelope-from ); Tue, 27 Aug 2024 21:10:11 +0000 Message-ID: Date: Tue, 27 Aug 2024 23:10:10 +0200 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 2/3] mm: add kmem_cache_create_rcu() Content-Language: en-US To: Christian Brauner , Jens Axboe , "Paul E. McKenney" , Roman Gushchin , Jann Horn , Linus Torvalds , linux-mm@kvack.org Cc: linux-fsdevel@vger.kernel.org References: <20240827-work-kmem_cache-rcu-v2-0-7bc9c90d5eef@kernel.org> <20240827-work-kmem_cache-rcu-v2-2-7bc9c90d5eef@kernel.org> From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSBWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBzdXNlLmN6PsLBlAQTAQoAPgIbAwULCQgHAwUVCgkICwUWAgMBAAIe AQIXgBYhBKlA1DSZLC6OmRA9UCJPp+fMgqZkBQJkBREIBQkRadznAAoJECJPp+fMgqZkNxIQ ALZRqwdUGzqL2aeSavbum/VF/+td+nZfuH0xeWiO2w8mG0+nPd5j9ujYeHcUP1edE7uQrjOC Gs9sm8+W1xYnbClMJTsXiAV88D2btFUdU1mCXURAL9wWZ8Jsmz5ZH2V6AUszvNezsS/VIT87 AmTtj31TLDGwdxaZTSYLwAOOOtyqafOEq+gJB30RxTRE3h3G1zpO7OM9K6ysLdAlwAGYWgJJ V4JqGsQ/lyEtxxFpUCjb5Pztp7cQxhlkil0oBYHkudiG8j1U3DG8iC6rnB4yJaLphKx57NuQ PIY0Bccg+r9gIQ4XeSK2PQhdXdy3UWBr913ZQ9AI2usid3s5vabo4iBvpJNFLgUmxFnr73SJ KsRh/2OBsg1XXF/wRQGBO9vRuJUAbnaIVcmGOUogdBVS9Sun/Sy4GNA++KtFZK95U7J417/J Hub2xV6Ehc7UGW6fIvIQmzJ3zaTEfuriU1P8ayfddrAgZb25JnOW7L1zdYL8rXiezOyYZ8Fm ZyXjzWdO0RpxcUEp6GsJr11Bc4F3aae9OZtwtLL/jxc7y6pUugB00PodgnQ6CMcfR/HjXlae h2VS3zl9+tQWHu6s1R58t5BuMS2FNA58wU/IazImc/ZQA+slDBfhRDGYlExjg19UXWe/gMcl De3P1kxYPgZdGE2eZpRLIbt+rYnqQKy8UxlszsBNBFsZNTUBCACfQfpSsWJZyi+SHoRdVyX5 J6rI7okc4+b571a7RXD5UhS9dlVRVVAtrU9ANSLqPTQKGVxHrqD39XSw8hxK61pw8p90pg4G /N3iuWEvyt+t0SxDDkClnGsDyRhlUyEWYFEoBrrCizbmahOUwqkJbNMfzj5Y7n7OIJOxNRkB IBOjPdF26dMP69BwePQao1M8Acrrex9sAHYjQGyVmReRjVEtv9iG4DoTsnIR3amKVk6si4Ea X/mrapJqSCcBUVYUFH8M7bsm4CSxier5ofy8jTEa/CfvkqpKThTMCQPNZKY7hke5qEq1CBk2 wxhX48ZrJEFf1v3NuV3OimgsF2odzieNABEBAAHCwXwEGAEKACYCGwwWIQSpQNQ0mSwujpkQ PVAiT6fnzIKmZAUCZAUSmwUJDK5EZgAKCRAiT6fnzIKmZOJGEACOKABgo9wJXsbWhGWYO7mD 8R8mUyJHqbvaz+yTLnvRwfe/VwafFfDMx5GYVYzMY9TWpA8psFTKTUIIQmx2scYsRBUwm5VI EurRWKqENcDRjyo+ol59j0FViYysjQQeobXBDDE31t5SBg++veI6tXfpco/UiKEsDswL1WAr tEAZaruo7254TyH+gydURl2wJuzo/aZ7Y7PpqaODbYv727Dvm5eX64HCyyAH0s6sOCyGF5/p eIhrOn24oBf67KtdAN3H9JoFNUVTYJc1VJU3R1JtVdgwEdr+NEciEfYl0O19VpLE/PZxP4wX PWnhf5WjdoNI1Xec+RcJ5p/pSel0jnvBX8L2cmniYnmI883NhtGZsEWj++wyKiS4NranDFlA HdDM3b4lUth1pTtABKQ1YuTvehj7EfoWD3bv9kuGZGPrAeFNiHPdOT7DaXKeHpW9homgtBxj 8aX/UkSvEGJKUEbFL9cVa5tzyialGkSiZJNkWgeHe+jEcfRT6pJZOJidSCdzvJpbdJmm+eED w9XOLH1IIWh7RURU7G1iOfEfmImFeC3cbbS73LQEFGe1urxvIH5K/7vX+FkNcr9ujwWuPE9b 1C2o4i/yZPLXIVy387EjA6GZMqvQUFuSTs/GeBcv0NjIQi8867H3uLjz+mQy63fAitsDwLmR EP+ylKVEKb0Q2A== In-Reply-To: <20240827-work-kmem_cache-rcu-v2-2-7bc9c90d5eef@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Level: X-Spamd-Result: default: False [-4.30 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_SEVEN(0.00)[8]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.cz:s=susede2_rsa,suse.cz:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.cz:mid] X-Spam-Score: -4.30 X-Spam-Flag: NO On 8/27/24 17:59, Christian Brauner wrote: > When a kmem cache is created with SLAB_TYPESAFE_BY_RCU the free pointer > must be located outside of the object because we don't know what part of > the memory can safely be overwritten as it may be needed to prevent > object recycling. > > That has the consequence that SLAB_TYPESAFE_BY_RCU may end up adding a > new cacheline. This is the case for .e.g, struct file. After having it > shrunk down by 40 bytes and having it fit in three cachelines we still > have SLAB_TYPESAFE_BY_RCU adding a fourth cacheline because it needs to > accomodate the free pointer and is hardware cacheline aligned. > > I tried to find ways to rectify this as struct file is pretty much > everywhere and having it use less memory is a good thing. So here's a > proposal. > > Signed-off-by: Christian Brauner So logistically patch 3 needs stuff in the vfs tree and having 1+2 in slab tree and 3 in vfs that depends on 1+2 elsewhere is infeasible, so it will be easiest for whole series to be in vfs, right? > --- > include/linux/slab.h | 9 ++++ > mm/slab.h | 1 + > mm/slab_common.c | 133 ++++++++++++++++++++++++++++++++++++--------------- > mm/slub.c | 17 ++++--- > 4 files changed, 114 insertions(+), 46 deletions(-) > > diff --git a/include/linux/slab.h b/include/linux/slab.h > index eb2bf4629157..5b2da2cf31a8 100644 > --- a/include/linux/slab.h > +++ b/include/linux/slab.h > @@ -212,6 +212,12 @@ enum _slab_flag_bits { > #define SLAB_NO_OBJ_EXT __SLAB_FLAG_UNUSED > #endif > > +/* > + * freeptr_t represents a SLUB freelist pointer, which might be encoded > + * and not dereferenceable if CONFIG_SLAB_FREELIST_HARDENED is enabled. > + */ > +typedef struct { unsigned long v; } freeptr_t; > + > /* > * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests. > * > @@ -242,6 +248,9 @@ struct kmem_cache *kmem_cache_create_usercopy(const char *name, > slab_flags_t flags, > unsigned int useroffset, unsigned int usersize, > void (*ctor)(void *)); > +struct kmem_cache *kmem_cache_create_rcu(const char *name, unsigned int size, > + unsigned int freeptr_offset, > + slab_flags_t flags); > void kmem_cache_destroy(struct kmem_cache *s); > int kmem_cache_shrink(struct kmem_cache *s); > > diff --git a/mm/slab.h b/mm/slab.h > index dcdb56b8e7f5..b05512a14f07 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -261,6 +261,7 @@ struct kmem_cache { > unsigned int object_size; /* Object size without metadata */ > struct reciprocal_value reciprocal_size; > unsigned int offset; /* Free pointer offset */ > + unsigned int rcu_freeptr_offset; /* Specific free pointer requested */ More precisely something like: Specific offset requested (if not UINT_MAX) ? > #ifdef CONFIG_SLUB_CPU_PARTIAL > /* Number of per cpu partial objects to keep around */ > unsigned int cpu_partial; > diff --git a/mm/slab_common.c b/mm/slab_common.c > index c8dd7e08c5f6..c4beff642fff 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -202,9 +202,10 @@ struct kmem_cache *find_mergeable(unsigned int size, unsigned int align, > } > > static struct kmem_cache *create_cache(const char *name, > - unsigned int object_size, unsigned int align, > - slab_flags_t flags, unsigned int useroffset, > - unsigned int usersize, void (*ctor)(void *)) > + unsigned int object_size, unsigned int freeptr_offset, > + unsigned int align, slab_flags_t flags, > + unsigned int useroffset, unsigned int usersize, > + void (*ctor)(void *)) > { > struct kmem_cache *s; > int err; > @@ -212,6 +213,12 @@ static struct kmem_cache *create_cache(const char *name, > if (WARN_ON(useroffset + usersize > object_size)) > useroffset = usersize = 0; > > + err = -EINVAL; > + if (freeptr_offset < UINT_MAX && freeptr_offset != UINT_MAX to be more obvious and match has_freeptr_offset() ? > + (freeptr_offset >= object_size || > + (freeptr_offset && !(flags & SLAB_TYPESAFE_BY_RCU)))) and here drop the "freeptr_offset &&" as zero is a valid value instead we could want alignment to sizeof(freeptr_t) if we were paranoid? > + goto out; The rest seems good to me now.