From patchwork Tue Aug 28 17:19:39 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 10578877 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 1EA895A4 for ; Tue, 28 Aug 2018 17:20:13 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 013B72A924 for ; Tue, 28 Aug 2018 17:20:09 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id E99FE2A92E; Tue, 28 Aug 2018 17:20:08 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 68BF92A924 for ; Tue, 28 Aug 2018 17:20:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726833AbeH1VMk (ORCPT ); Tue, 28 Aug 2018 17:12:40 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:36146 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726996AbeH1VMj (ORCPT ); Tue, 28 Aug 2018 17:12:39 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 3406580C3C16; Tue, 28 Aug 2018 17:19:59 +0000 (UTC) Received: from llong.com (ovpn-123-12.rdu2.redhat.com [10.10.123.12]) by smtp.corp.redhat.com (Postfix) with ESMTP id A016C63F37; Tue, 28 Aug 2018 17:19:57 +0000 (UTC) From: Waiman Long To: Alexander Viro , Jonathan Corbet Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-doc@vger.kernel.org, "Luis R. Rodriguez" , Kees Cook , Linus Torvalds , Jan Kara , "Paul E. McKenney" , Andrew Morton , Ingo Molnar , Miklos Szeredi , Matthew Wilcox , Larry Woodman , James Bottomley , "Wangkai (Kevin C)" , Michal Hocko , Waiman Long Subject: [PATCH 1/2] fs/dcache: Track & report number of negative dentries Date: Tue, 28 Aug 2018 13:19:39 -0400 Message-Id: <1535476780-5773-2-git-send-email-longman@redhat.com> In-Reply-To: <1535476780-5773-1-git-send-email-longman@redhat.com> References: <1535476780-5773-1-git-send-email-longman@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Tue, 28 Aug 2018 17:19:59 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Tue, 28 Aug 2018 17:19:59 +0000 (UTC) for IP:'10.11.54.5' DOMAIN:'int-mx05.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'longman@redhat.com' RCPT:'' Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP The current dentry number tracking code doesn't distinguish between positive & negative dentries. It just reports the total number of dentries in the LRU lists. As excessive number of negative dentries can have an impact on system performance, it will be wise to track the number of positive and negative dentries separately. This patch adds tracking for the total number of negative dentries in the system LRU lists and reports it in the /proc/sys/fs/dentry-state file. The number, however, does not include negative dentries that are in flight but not in the LRU yet. The number of positive dentries in the LRU lists can be roughly found by subtracting the number of negative dentries from the total. Signed-off-by: Waiman Long --- Documentation/sysctl/fs.txt | 19 +++++++++++++------ fs/dcache.c | 45 +++++++++++++++++++++++++++++++++++++++++++++ include/linux/dcache.h | 7 ++++--- 3 files changed, 62 insertions(+), 9 deletions(-) diff --git a/Documentation/sysctl/fs.txt b/Documentation/sysctl/fs.txt index 819caf8..118bb93 100644 --- a/Documentation/sysctl/fs.txt +++ b/Documentation/sysctl/fs.txt @@ -63,19 +63,26 @@ struct { int nr_unused; int age_limit; /* age in seconds */ int want_pages; /* pages requested by system */ - int dummy[2]; + int nr_negative; /* # of unused negative dentries */ + int dummy; } dentry_stat = {0, 0, 45, 0,}; --------------------------------------------------------------- +-------------------------------------------------------------- + +Dentries are dynamically allocated and deallocated. + +nr_dentry shows the total number of dentries allocated (active ++ unused). nr_unused shows the number of dentries that are not +actively used, but are saved in the LRU list for future reuse. -Dentries are dynamically allocated and deallocated, and -nr_dentry seems to be 0 all the time. Hence it's safe to -assume that only nr_unused, age_limit and want_pages are -used. Nr_unused seems to be exactly what its name says. Age_limit is the age in seconds after which dcache entries can be reclaimed when memory is short and want_pages is nonzero when shrink_dcache_pages() has been called and the dcache isn't pruned yet. +nr_negative shows the number of unused dentries that are also +negative dentries which do not mapped to actual files if negative +dentries tracking is enabled. + ============================================================== dquot-max & dquot-nr: diff --git a/fs/dcache.c b/fs/dcache.c index 2e7e8d8..69f5541 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -119,6 +119,7 @@ struct dentry_stat_t dentry_stat = { static DEFINE_PER_CPU(long, nr_dentry); static DEFINE_PER_CPU(long, nr_dentry_unused); +static DEFINE_PER_CPU(long, nr_dentry_neg); #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS) @@ -152,11 +153,22 @@ static long get_nr_dentry_unused(void) return sum < 0 ? 0 : sum; } +static long get_nr_dentry_neg(void) +{ + int i; + long sum = 0; + + for_each_possible_cpu(i) + sum += per_cpu(nr_dentry_neg, i); + return sum < 0 ? 0 : sum; +} + int proc_nr_dentry(struct ctl_table *table, int write, void __user *buffer, size_t *lenp, loff_t *ppos) { dentry_stat.nr_dentry = get_nr_dentry(); dentry_stat.nr_unused = get_nr_dentry_unused(); + dentry_stat.nr_negative = get_nr_dentry_neg(); return proc_doulongvec_minmax(table, write, buffer, lenp, ppos); } #endif @@ -214,6 +226,28 @@ static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char #endif +static inline void __neg_dentry_dec(struct dentry *dentry) +{ + this_cpu_dec(nr_dentry_neg); +} + +static inline void neg_dentry_dec(struct dentry *dentry) +{ + if (unlikely(d_is_negative(dentry))) + __neg_dentry_dec(dentry); +} + +static inline void __neg_dentry_inc(struct dentry *dentry) +{ + this_cpu_inc(nr_dentry_neg); +} + +static inline void neg_dentry_inc(struct dentry *dentry) +{ + if (unlikely(d_is_negative(dentry))) + __neg_dentry_inc(dentry); +} + static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *ct, unsigned tcount) { /* @@ -331,6 +365,8 @@ static inline void __d_clear_type_and_inode(struct dentry *dentry) flags &= ~(DCACHE_ENTRY_TYPE | DCACHE_FALLTHRU); WRITE_ONCE(dentry->d_flags, flags); dentry->d_inode = NULL; + if (dentry->d_flags & DCACHE_LRU_LIST) + __neg_dentry_inc(dentry); } static void dentry_free(struct dentry *dentry) @@ -395,6 +431,7 @@ static void d_lru_add(struct dentry *dentry) dentry->d_flags |= DCACHE_LRU_LIST; this_cpu_inc(nr_dentry_unused); WARN_ON_ONCE(!list_lru_add(&dentry->d_sb->s_dentry_lru, &dentry->d_lru)); + neg_dentry_inc(dentry); } static void d_lru_del(struct dentry *dentry) @@ -403,6 +440,7 @@ static void d_lru_del(struct dentry *dentry) dentry->d_flags &= ~DCACHE_LRU_LIST; this_cpu_dec(nr_dentry_unused); WARN_ON_ONCE(!list_lru_del(&dentry->d_sb->s_dentry_lru, &dentry->d_lru)); + neg_dentry_dec(dentry); } static void d_shrink_del(struct dentry *dentry) @@ -433,6 +471,7 @@ static void d_lru_isolate(struct list_lru_one *lru, struct dentry *dentry) dentry->d_flags &= ~DCACHE_LRU_LIST; this_cpu_dec(nr_dentry_unused); list_lru_isolate(lru, &dentry->d_lru); + neg_dentry_dec(dentry); } static void d_lru_shrink_move(struct list_lru_one *lru, struct dentry *dentry, @@ -441,6 +480,7 @@ static void d_lru_shrink_move(struct list_lru_one *lru, struct dentry *dentry, D_FLAG_VERIFY(dentry, DCACHE_LRU_LIST); dentry->d_flags |= DCACHE_SHRINK_LIST; list_lru_isolate_move(lru, &dentry->d_lru, list); + neg_dentry_dec(dentry); } /** @@ -1840,6 +1880,11 @@ static void __d_instantiate(struct dentry *dentry, struct inode *inode) WARN_ON(d_in_lookup(dentry)); spin_lock(&dentry->d_lock); + /* + * Decrement negative dentry count if it was in the LRU list. + */ + if (dentry->d_flags & DCACHE_LRU_LIST) + __neg_dentry_dec(dentry); hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry); raw_write_seqcount_begin(&dentry->d_seq); __d_set_inode_and_type(dentry, inode, add_flags); diff --git a/include/linux/dcache.h b/include/linux/dcache.h index ef4b70f..df942e5 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -62,9 +62,10 @@ struct qstr { struct dentry_stat_t { long nr_dentry; long nr_unused; - long age_limit; /* age in seconds */ - long want_pages; /* pages requested by system */ - long dummy[2]; + long age_limit; /* age in seconds */ + long want_pages; /* pages requested by system */ + long nr_negative; /* # of unused negative dentries */ + long dummy; }; extern struct dentry_stat_t dentry_stat;