From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id ACFA3C6FD20 for ; Fri, 24 Mar 2023 09:03:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232009AbjCXJDb (ORCPT ); Fri, 24 Mar 2023 05:03:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44456 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231621AbjCXJD3 (ORCPT ); Fri, 24 Mar 2023 05:03:29 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3E3851BFE for ; Fri, 24 Mar 2023 02:03:27 -0700 (PDT) Received: from dggpemm100009.china.huawei.com (unknown [172.30.72.57]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4PjbnV1qFQzrWGT; Fri, 24 Mar 2023 17:02:22 +0800 (CST) Received: from [10.174.179.24] (10.174.179.24) by dggpemm100009.china.huawei.com (7.185.36.113) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.21; Fri, 24 Mar 2023 17:03:25 +0800 Subject: Re: [PATCH -next v6 2/2] mm/zswap: delay the initializaton of zswap To: Christoph Hellwig References: <20230322102006.780624-1-liushixin2@huawei.com> <20230322102006.780624-3-liushixin2@huawei.com> <20230323080443.GC20444@lst.de> CC: Seth Jennings , Dan Streetman , Vitaly Wool , Andrew Morton , Nathan Chancellor , , From: Liu Shixin Message-ID: Date: Fri, 24 Mar 2023 17:03:24 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: <20230323080443.GC20444@lst.de> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.179.24] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To dggpemm100009.china.huawei.com (7.185.36.113) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/3/23 16:04, Christoph Hellwig wrote: > On Wed, Mar 22, 2023 at 06:20:06PM +0800, Liu Shixin wrote: >> Since some users may not use zswap, the zswap_pool is wasted. Save memory >> by delaying the initialization of zswap until enabled. >> >> Signed-off-by: Liu Shixin >> --- >> mm/zswap.c | 51 +++++++++++++++++++++++++++++++++++++++++---------- >> 1 file changed, 41 insertions(+), 10 deletions(-) >> >> diff --git a/mm/zswap.c b/mm/zswap.c >> index 09fa956920fa..3aed3b26524a 100644 >> --- a/mm/zswap.c >> +++ b/mm/zswap.c >> @@ -81,6 +81,8 @@ static bool zswap_pool_reached_full; >> >> #define ZSWAP_PARAM_UNSET "" >> >> +static int zswap_setup(void); >> + >> /* Enable/disable zswap */ >> static bool zswap_enabled = IS_ENABLED(CONFIG_ZSWAP_DEFAULT_ON); >> static int zswap_enabled_param_set(const char *, >> @@ -220,6 +222,9 @@ static bool zswap_init_started; >> /* fatal error during init */ >> static bool zswap_init_failed; >> >> +/* used to ensure the integrity of initialization */ >> +static DEFINE_MUTEX(zswap_init_lock); >> + >> /* init completed, but couldn't create the initial pool */ >> static bool zswap_has_pool; >> >> @@ -272,13 +277,13 @@ static void zswap_update_total_size(void) >> **********************************/ >> static struct kmem_cache *zswap_entry_cache; >> >> -static int __init zswap_entry_cache_create(void) >> +static int zswap_entry_cache_create(void) >> { >> zswap_entry_cache = KMEM_CACHE(zswap_entry, 0); >> return zswap_entry_cache == NULL; >> } > Please add a cleanup patch to remove this helper first, it just > massivel confuses the reader. I will, thanks. > >> -static void __init zswap_entry_cache_destroy(void) >> +static void zswap_entry_cache_destroy(void) >> { >> kmem_cache_destroy(zswap_entry_cache); >> } > Same here. > >> @@ -663,7 +668,7 @@ static struct zswap_pool *zswap_pool_create(char *type, char *compressor) >> return NULL; >> } >> >> -static __init struct zswap_pool *__zswap_pool_create_fallback(void) >> +static struct zswap_pool *__zswap_pool_create_fallback(void) >> { >> bool has_comp, has_zpool; >> >> @@ -784,8 +789,15 @@ static int __zswap_param_set(const char *val, const struct kernel_param *kp, >> /* if this is load-time (pre-init) param setting, >> * don't create a pool; that's done during init. >> */ >> - if (!zswap_init_started) >> - return param_set_charp(s, kp); >> + if (!zswap_init_started) { >> + mutex_lock(&zswap_init_lock); >> + if (!zswap_init_started) { >> + ret = param_set_charp(s, kp); >> + mutex_unlock(&zswap_init_lock); >> + return ret; >> + } >> + mutex_unlock(&zswap_init_lock); >> + } > Just take the lock around the whole function. No need to micro-optimize > setting a kernel paramter. I will, thanks. > >> @@ -884,6 +896,15 @@ static int zswap_enabled_param_set(const char *val, >> if (res == *(bool *)kp->arg) >> return 0; >> >> + if (!zswap_init_started && (system_state == SYSTEM_RUNNING)) { > No need for the inner braces. But directly looking at > SYSTEM_RUNNING, especially without a comment is a bit of a mess. > Is there any better way to deal with this? I have no idea about better way. > > Also the zswap_init_started variable name has always been a bit > confusing. If everything around it takes zswap_init_lock now, > it can be replaced with a check for successful zswap initialization > as all the initializtion is covered by the lock. That would really > help to clean up the code. I will, thanks. > >> +static int zswap_debugfs_init(void) >> { >> if (!debugfs_initialized()) >> return -ENODEV; >> @@ -1482,7 +1503,7 @@ static int __init zswap_debugfs_init(void) >> return 0; >> } >> #else >> -static int __init zswap_debugfs_init(void) >> +static int zswap_debugfs_init(void) > Is there any reason to not just always initialize debugfs and > only defer the expensive allocations? It seems there is no need to initialize debugfs if zswap is not used. > > . >