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Mon, 31 May 2021 06:55:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 1DC93C433F1 Subject: Re: [PATCH v7] mm: slub: move sysfs slab alloc/free interfaces to debugfs To: Vlastimil Babka , 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> <86d843f0-bbef-7c3b-6b6a-5d6b32434bee@suse.cz> From: Faiyaz Mohammed Message-ID: Date: Mon, 31 May 2021 12:25:08 +0530 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.10.2 MIME-Version: 1.0 In-Reply-To: <86d843f0-bbef-7c3b-6b6a-5d6b32434bee@suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=mg.codeaurora.org header.s=smtp header.b=jfWPKX2q; dmarc=none; spf=pass (imf05.hostedemail.com: domain of bounce@mg.codeaurora.org designates 69.72.43.7 as permitted sender) smtp.mailfrom=bounce@mg.codeaurora.org X-Stat-Signature: pazuebhh5hkqbnzhfbyr1985tejyppds X-Rspamd-Queue-Id: AEB33E000249 X-Rspamd-Server: rspam02 X-HE-Tag: 1622444757-168267 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 5/26/2021 5:08 PM, Vlastimil Babka wrote: > 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. >> >> To overcome this issues, move the alloc_calls and free_calls implemeation >> to debugfs. >> >> Rename the alloc_calls/free_calls to alloc_traces/free_traces, >> to be inline with what it does. >> >> Reported-by: kernel test robot >> Reported-by: Dan Carpenter > > These were IIRC bot reports for some bugs in the previous versions, so keeping > the Reported-by: for the whole patch is misleading - these were not reports for > the sysfs issues this patch fixes by moving the files to debugfs. > Yes, I will update in next patch version. >> 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/ >> >> changes in v5: >> - https://lore.kernel.org/linux-mm/1620296523-21922-1-git-send-email-faiyazm@codeaurora.org/ >> >> changes in v4: >> - https://lore.kernel.org/linux-mm/1618583239-18124-1-git-send-email-faiyazm@codeaurora.org/ >> >> changes in v3: >> - https://lore.kernel.org/linux-mm/1617712064-12264-1-git-send-email-faiyazm@codeaurora.org/ >> >> changes in v2: >> - https://lore.kernel.org/linux-mm/3ac1d3e6-6207-96ad-16a1-0f5139d8b2b5@codeaurora.org/ >> >> changes in v1: >> - https://lore.kernel.org/linux-mm/1610443287-23933-1-git-send-email-faiyazm@codeaurora.org/ >> >> 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: > I think I missed one thing, when CONFIG_SLUB_DEBUG_ON enable or slub_debug is pass through command line __kmem_cache_alias() will return null, so no symlinks will be created even if CONFIG_SLAB_MERGE_DEFAULT is enable and to store user data we need to enable CONFIG_SLUB_DEBUG_ON or pass slub_debug through command line. >> @@ -4525,6 +4535,8 @@ __kmem_cache_alias(const char *name, unsigned int size, unsigned int align, >> s->refcount--; >> s = NULL; >> } >> + >> + debugfs_slab_alias(s, name); > > Here you might be calling debugfs_slab_alias() with NULL if the > sysfs_slab_alias() above returned true. > I think we can drop debugfs_slab_alias implementation. >> } >> >> return s; > > ... > >> +static int __init slab_debugfs_init(void) >> +{ >> + struct kmem_cache *s; >> + >> + slab_debugfs_root = debugfs_create_dir("slab", NULL); >> + >> + slab_state = FULL; >> + >> + list_for_each_entry(s, &slab_caches, list) >> + debugfs_slab_add(s); >> + >> + while (alias_list) { >> + struct saved_alias *al = 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 actually > find an unflushed list. I think you > need to use a separate list for debugfs (simpler) or a shared list with both > sysfs and debugfs processing (probably more complicated). > same here, I think we can drop the debugfs alias change. > And finally a question, perhaps also for Greg. With sysfs, we hand out the > lifecycle of struct kmem_cache to sysfs, to ensure we are not reading sysfs > 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 the cache? > >> + >> + alias_list = alias_list->next; >> + >> + debugfs_slab_alias(al->s, al->name); >> + >> + kfree(al); >> + } >> + >> + return 0; >> + >> +} >> +__initcall(slab_debugfs_init); >> +#endif >> /* >> * The /proc/slabinfo ABI >> */ >> >