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[2003:cb:c702:5700:cb5b:f73a:c650:1d9]) by smtp.gmail.com with ESMTPSA id s9-20020a5d4ec9000000b002cde25fba30sm3226133wrv.1.2023.04.14.02.37.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 14 Apr 2023 02:38:00 -0700 (PDT) Message-ID: <62881f72-f8e8-f6cf-505d-2dd8cdef3643@redhat.com> Date: Fri, 14 Apr 2023 11:37:58 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.1 Subject: Re: [PATCH v3 2/2] modules/kmod: replace implementation with a semaphore To: Luis Chamberlain , patches@lists.linux.dev, linux-modules@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, pmladek@suse.com, petr.pavlu@suse.com, prarit@redhat.com, torvalds@linux-foundation.org, gregkh@linuxfoundation.org, rafael@kernel.org Cc: christophe.leroy@csgroup.eu, tglx@linutronix.de, peterz@infradead.org, song@kernel.org, rppt@kernel.org, dave@stgolabs.net, willy@infradead.org, vbabka@suse.cz, mhocko@suse.com, dave.hansen@linux.intel.com, colin.i.king@gmail.com, jim.cromie@gmail.com, catalin.marinas@arm.com, jbaron@akamai.com, rick.p.edgecombe@intel.com References: <20230414051349.1986744-1-mcgrof@kernel.org> <20230414051349.1986744-3-mcgrof@kernel.org> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230414051349.1986744-3-mcgrof@kernel.org> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: 5qshmpnjwcebacswzzizq9bep18fndta X-Rspamd-Queue-Id: A25E940003 X-HE-Tag: 1681465086-44927 X-HE-Meta: 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 Av8g02LI 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 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 14.04.23 07:13, Luis Chamberlain wrote: > Simplify the concurrency delimiter we use for kmod with the semaphore. > I had used the kmod strategy to try to implement a similar concurrency > delimiter for the kernel_read*() calls from the finit_module() path > so to reduce vmalloc() memory pressure. That effort didn't provide yet > conclusive results, but one thing that became clear is we can use > the suggested alternative solution with semaphores which Linus hinted > at instead of using the atomic / wait strategy. > > I've stress tested this with kmod test 0008: > > time /data/linux-next/tools/testing/selftests/kmod/kmod.sh -t 0008 > > And I get only a *slight* delay. That delay however is small, a few > seconds for a full test loop run that runs 150 times, for about ~30-40 > seconds. The small delay is worth the simplfication IMHO. > > Signed-off-by: Luis Chamberlain > --- > kernel/module/kmod.c | 26 +++++++------------------- > 1 file changed, 7 insertions(+), 19 deletions(-) > > diff --git a/kernel/module/kmod.c b/kernel/module/kmod.c > index b717134ebe17..5899083436a3 100644 > --- a/kernel/module/kmod.c > +++ b/kernel/module/kmod.c > @@ -40,8 +40,7 @@ > * effect. Systems like these are very unlikely if modules are enabled. > */ > #define MAX_KMOD_CONCURRENT 50 > -static atomic_t kmod_concurrent_max = ATOMIC_INIT(MAX_KMOD_CONCURRENT); > -static DECLARE_WAIT_QUEUE_HEAD(kmod_wq); > +static DEFINE_SEMAPHORE(kmod_concurrent_max, MAX_KMOD_CONCURRENT); > > /* > * This is a restriction on having *all* MAX_KMOD_CONCURRENT threads > @@ -148,29 +147,18 @@ int __request_module(bool wait, const char *fmt, ...) > if (ret) > return ret; > > - if (atomic_dec_if_positive(&kmod_concurrent_max) < 0) { > - pr_warn_ratelimited("request_module: kmod_concurrent_max (%u) close to 0 (max_modprobes: %u), for module %s, throttling...", > - atomic_read(&kmod_concurrent_max), > - MAX_KMOD_CONCURRENT, module_name); > - ret = wait_event_killable_timeout(kmod_wq, > - atomic_dec_if_positive(&kmod_concurrent_max) >= 0, > - MAX_KMOD_ALL_BUSY_TIMEOUT * HZ); > - if (!ret) { > - pr_warn_ratelimited("request_module: modprobe %s cannot be processed, kmod busy with %d threads for more than %d seconds now", > - module_name, MAX_KMOD_CONCURRENT, MAX_KMOD_ALL_BUSY_TIMEOUT); > - return -ETIME; > - } else if (ret == -ERESTARTSYS) { > - pr_warn_ratelimited("request_module: sigkill sent for modprobe %s, giving up", module_name); > - return ret; > - } > + ret = down_timeout(&kmod_concurrent_max, MAX_KMOD_ALL_BUSY_TIMEOUT * HZ); > + if (ret) { > + pr_warn_ratelimited("request_module: modprobe %s cannot be processed, kmod busy with %d threads for more than %d seconds now", > + module_name, MAX_KMOD_CONCURRENT, MAX_KMOD_ALL_BUSY_TIMEOUT); > + return ret; > } > > trace_module_request(module_name, wait, _RET_IP_); > > ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC); > > - atomic_inc(&kmod_concurrent_max); > - wake_up(&kmod_wq); > + up(&kmod_concurrent_max); > > return ret; > } Reviewed-by: David Hildenbrand -- Thanks, David / dhildenb