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Wed, 26 May 2021 11:38:55 +0000 (UTC) To: Faiyaz Mohammed , cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, greg@kroah.com, glittao@gmail.com Cc: vinmenon@codeaurora.org References: <1621928285-751-1-git-send-email-faiyazm@codeaurora.org> From: Vlastimil Babka Subject: Re: [PATCH v7] mm: slub: move sysfs slab alloc/free interfaces to debugfs Message-ID: <86d843f0-bbef-7c3b-6b6a-5d6b32434bee@suse.cz> Date: Wed, 26 May 2021 13:38:55 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.2 MIME-Version: 1.0 In-Reply-To: <1621928285-751-1-git-send-email-faiyazm@codeaurora.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=suse.cz header.s=susede2_rsa header.b=vZBTntci; dkim=pass header.d=suse.cz header.s=susede2_ed25519 header.b=ftHQakNk; spf=pass (imf17.hostedemail.com: domain of vbabka@suse.cz designates 195.135.220.28 as permitted sender) smtp.mailfrom=vbabka@suse.cz; dmarc=none X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 2E33E40F8C07 X-Stat-Signature: 35fhdfxonxuhoyhxesaxejj4frbohxw9 X-HE-Tag: 1622029132-12108 Content-Transfer-Encoding: quoted-printable 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: On 5/25/21 9:38 AM, Faiyaz Mohammed wrote: > alloc_calls and free_calls implementation in sysfs have two issues, > one is PAGE_SIZE limitiation of sysfs and other is it does not adhere > to "one value per file" rule. >=20 > To overcome this issues, move the alloc_calls and free_calls implemeati= on > to debugfs. >=20 > Rename the alloc_calls/free_calls to alloc_traces/free_traces, > to be inline with what it does. >=20 > Reported-by: kernel test robot > Reported-by: Dan Carpenter These were IIRC bot reports for some bugs in the previous versions, so ke= eping the Reported-by: for the whole patch is misleading - these were not repor= ts for the sysfs issues this patch fixes by moving the files to debugfs. > Signed-off-by: Faiyaz Mohammed > --- > changes in V7: > - Drop the older alloc_calls and free_calls interface. > changes in v6: > - https://lore.kernel.org/linux-mm/1621341949-26762-1-git-send-= email-faiyazm@codeaurora.org/ >=20 > changes in v5: > - https://lore.kernel.org/linux-mm/1620296523-21922-1-git-send-= email-faiyazm@codeaurora.org/ >=20 > changes in v4: > - https://lore.kernel.org/linux-mm/1618583239-18124-1-git-send-= email-faiyazm@codeaurora.org/ >=20 > changes in v3: > - https://lore.kernel.org/linux-mm/1617712064-12264-1-git-send-= email-faiyazm@codeaurora.org/ >=20 > changes in v2: > - https://lore.kernel.org/linux-mm/3ac1d3e6-6207-96ad-16a1-0f51= 39d8b2b5@codeaurora.org/ >=20 > changes in v1: > - https://lore.kernel.org/linux-mm/1610443287-23933-1-git-send-= email-faiyazm@codeaurora.org/ >=20 > include/linux/slub_def.h | 8 ++ > mm/slab_common.c | 9 ++ > mm/slub.c | 353 ++++++++++++++++++++++++++++++++++-----= -------- > 3 files changed, 276 insertions(+), 94 deletions(-) I don't see any of the symlinks under /sys/kernel/debug/slab/, so I think= the aliases handling code is wrong, and I can see at least two reasons why it= could be: > @@ -4525,6 +4535,8 @@ __kmem_cache_alias(const char *name, unsigned int= size, unsigned int align, > s->refcount--; > s =3D NULL; > } > + > + debugfs_slab_alias(s, name); Here you might be calling debugfs_slab_alias() with NULL if the sysfs_slab_alias() above returned true. > } > =20 > return s; ... > +static int __init slab_debugfs_init(void) > +{ > + struct kmem_cache *s; > + > + slab_debugfs_root =3D debugfs_create_dir("slab", NULL); > + > + slab_state =3D FULL; > + > + list_for_each_entry(s, &slab_caches, list) > + debugfs_slab_add(s); > + > + while (alias_list) { > + struct saved_alias *al =3D alias_list; alias_list a single list and both slab_sysfs_init() and slab_debugfs_init= () flush it. So only the init call that happens to be called first, does act= ually find an unflushed list. I think you need to use a separate list for debugfs (simpler) or a shared list with b= oth sysfs and debugfs processing (probably more complicated). And finally a question, perhaps also for Greg. With sysfs, we hand out th= e lifecycle of struct kmem_cache to sysfs, to ensure we are not reading sys= fs files of a cache that has been removed. But with debugfs, what are the guarantees that things won't blow up when = a debugfs file is being read while somebody calls kmem_cache_destroy() on t= he cache? > + > + alias_list =3D alias_list->next; > + > + debugfs_slab_alias(al->s, al->name); > + > + kfree(al); > + } > + > + return 0; > + > +} > +__initcall(slab_debugfs_init); > +#endif > /* > * The /proc/slabinfo ABI > */ >=20