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b=fKMMmzgD8UZAY4iQDNzHsoe/vm62FJ8khvmHljKlL+8k75A8GjRKAIn6MxudSwOUc vHot8rNwI2vg53sgSyhGIYosr7n0Rlje8aG0MY/sPJh3bTMrzho8hN+4dErmvffD7D cq0FMFsXL9W1mLRSQ3UnyxIN/3E0oNP5b05tKLJ3zZzX1+5Qzu9a6z2oWqci1Cah0e DPjHAfrR+PWcfNifWNbVRkvz+r26Us9sLjTUH3aMr3nyCp4613zqvLVP6fsr+OtRLB z7P60p8v64kv+j/P8AEXSdaFJ+1t8aimnb108Fbix2cfryCHs9nudMfOxH2yYrwP/Y 3y9/J0YyqjMnA== Message-ID: Date: Thu, 16 Jul 2026 17:08:00 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 12/12] mm/slab: stop allocating objcg pointers when unnecessary Content-Language: en-US To: Suren Baghdasaryan Cc: Harry Yoo , Hao Li , Shakeel Butt , Alexander Potapenko , Marco Elver , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org References: <20260715-b4-objext_split-v1-0-9a49c4ccf4c3@kernel.org> <20260715-b4-objext_split-v1-12-9a49c4ccf4c3@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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 BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 5DAC4100012 X-Stat-Signature: zikjn33oi6nfmt65qf6gsd6nhik6cigd X-HE-Tag: 1784214486-541090 X-HE-Meta: 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 Ko8jbHYE A2o5KKc0eHMzs4MWKxNNWmicLBRIKFh+vLflLHtPRPnhDpfhaBjYZEQFATe20HM7wd/9vsD/c679pw5qjpwiuC3QNr7fc+eOzU66ezTBDIOuC8RKnSSxDVJvFqZqPnupyVwFc6mLAjMyxxqZSR6/D+0sJZVY0ey3ui1tp3YqVwfNu44DRArHZr8EdY76lnT9qSQ3FuEmqipzeVKFTbLgI8NQaQByHgrx+uukAoc/ce0Qgi7FlKOtheKxra+pu1mN1SjF7 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/16/26 06:46, Suren Baghdasaryan wrote: > Maybe now we should rename static_obj_ext_size() to > static_obj_ext_max_size() as it reflects the max possible size of > slabobj_ext? Hm with _max_size() it doesn't have to be called static_ anymore? But maybe we can get rid of it completely. The only caller is calculate_sizes(): #if defined(CONFIG_SLAB_OBJ_EXT) && defined(CONFIG_64BIT) if (slab_args_unmergeable(args, s->flags) && (aligned_size - size >= static_obj_ext_size())) s->flags |= SLAB_OBJ_EXT_IN_OBJ; #endif We don't have slab pointer to pass to static_obj_ext_max_size(). But we should be able to figure it out from the cache via cache_needs_objcg(). So we'd need cache_obj_ext_size()? The static max size here works, but may prevent SLAB_OBJ_EXT_IN_OBJ needlessly if padding can only fit codetag_ref and not objcg, but we don't need objcg. Which is probably only theoretical at this point as kmalloc_normal caches (that have no objcg) have no padding, at least without slab_debug. But still. >> + size_t sz = 0; >> + >> + if (slab_needs_objcg(slab)) >> + sz += 1; >> + >> + if (slab_obj_ext_has_codetag()) >> + sz += 1; >> + >> + return sizeof(struct slabobj_ext) * sz; >> } >> >> #ifdef CONFIG_SLAB_OBJ_EXT >> @@ -741,7 +749,7 @@ static inline struct obj_cgroup **slab_obj_ext_objcgp(struct slabobj_ext *obj_ex >> static inline union codetag_ref * >> slab_obj_ext_codetag_ref(struct slab *slab, struct slabobj_ext *obj_ext) >> { >> - if (IS_ENABLED(CONFIG_MEMCG)) >> + if (slab_needs_objcg(slab)) >> obj_ext += 1; >> >> return &obj_ext->_ctref; >> diff --git a/mm/slub.c b/mm/slub.c >> index 771d73abacb6..09c4931e5435 100644 >> --- a/mm/slub.c >> +++ b/mm/slub.c >> @@ -2503,6 +2503,9 @@ void memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p, >> if (likely(!obj_exts)) >> return; >> >> + if (!slab_needs_objcg(slab)) >> + return; >> + >> get_slab_obj_exts(obj_exts); >> __memcg_slab_free_hook(s, slab, p, objects, obj_exts); >> put_slab_obj_exts(obj_exts); >> >> -- >> 2.55.0 >>