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Tue, 26 Mar 2024 21:42:18 +0800 (CST) From: Kemeng Shi To: tytso@mit.edu, adilger.kernel@dilger.ca, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org Cc: jack@suse.cz, ojaswin@linux.ibm.com, ritesh.list@gmail.com Subject: [PATCH 3/5] ext4: call ext4_mb_mark_free_simple in mb_mark_used to clear bits Date: Wed, 27 Mar 2024 05:38:21 +0800 Message-Id: <20240326213823.528302-4-shikemeng@huaweicloud.com> X-Mailer: git-send-email 2.30.0 In-Reply-To: <20240326213823.528302-1-shikemeng@huaweicloud.com> References: <20240326213823.528302-1-shikemeng@huaweicloud.com> Precedence: bulk X-Mailing-List: linux-ext4@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-CM-TRANSID: cCh0CgCHowy00AJmmQiSIA--.63567S5 X-Coremail-Antispam: 1UD129KBjvJXoWxAFWxWw4fZF1fuF1furWfZrb_yoWrWr17pF W3ZrWfGr40vwn29F4UG3WjgF1F93y8ta45Jas3Ww1rWwnxJryFvFn5KF13Z3WvvrZ3XFyF yr4UuFy3Krs7KFDanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUBjb4IE77IF4wAFF20E14v26rWj6s0DM7CY07I20VC2zVCF04k2 6cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M280x2IEY4vEnII2IxkI6r1a6r45M2 8IrcIa0xkI8VA2jI8067AKxVWUWwA2048vs2IY020Ec7CjxVAFwI0_Xr0E3s1l8cAvFVAK 0II2c7xJM28CjxkF64kEwVA0rcxSw2x7M28EF7xvwVC0I7IYx2IY67AKxVW7JVWDJwA2z4 x0Y4vE2Ix0cI8IcVCY1x0267AKxVWxJVW8Jr1l84ACjcxK6I8E87Iv67AKxVW0oVCq3wA2 z4x0Y4vEx4A2jsIEc7CjxVAFwI0_GcCE3s1le2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4 xG64xvF2IEw4CE5I8CrVC2j2WlYx0E2Ix0cI8IcVAFwI0_JrI_JrylYx0Ex4A2jsIE14v2 6r1j6r4UMcvjeVCFs4IE7xkEbVWUJVW8JwACjcxG0xvY0x0EwIxGrwCF04k20xvY0x0EwI xGrwCFx2IqxVCFs4IE7xkEbVWUJVW8JwC20s026c02F40E14v26r1j6r18MI8I3I0E7480 Y4vE14v26r106r1rMI8E67AF67kF1VAFwI0_JF0_Jw1lIxkGc2Ij64vIr41lIxAIcVC0I7 IYx2IY67AKxVWUJVWUCwCI42IY6xIIjxv20xvEc7CjxVAFwI0_Gr0_Cr1lIxAIcVCF04k2 6cxKx2IYs7xG6r1j6r1xMIIF0xvEx4A2jsIE14v26r1j6r4UMIIF0xvEx4A2jsIEc7CjxV AFwI0_Gr0_Gr1UYxBIdaVFxhVjvjDU0xZFpf9x07j2FAJUUUUU= X-CM-SenderInfo: 5vklyvpphqwq5kxd4v5lfo033gof0z/ Function ext4_mb_mark_free_simple could search order for bit clearing in O(1) cost while mb_mark_used will search order in O(distance from chunk order to target order) and introduce unnecessary bit flips. Consider we have 4 continuous free bits and going to mark bit 0-2 inuse. initial state of buddy bitmap: order 2 | 0 | order 1 | 1 | 1 | order 0 | 1 | 1 | 1 | 1 | mark whole chunk inuse order 2 | 1 | order 1 | 1 | 1 | order 0 | 1 | 1 | 1 | 1 | split chunk to order 1 order 2 | 1 | order 1 | 0 | 0 | order 0 | 1 | 1 | 1 | 1 | set the first bit in order 1 to mark bit 0-1 inuse set the second bit in order 1 for split order 2 | 1 | order 1 | 1 | 1 | order 0 | 1 | 1 | 1 | 1 | step 3: split the second bit in order 1 to order 0 order 2 | 1 | order 1 | 1 | 1 | order 0 | 1 | 1 | 0 | 0 | step 4: set the third bit in order 0 to mark bit 2 inuse. order 2 | 1 | order 1 | 1 | 1 | order 0 | 1 | 1 | 1 | 0 | There are two unnecessary splits and three unnecessary bit flips. With ext4_mb_mark_free_simple, we will clear the 4th bit in order 0 with O(1) search and no extra bit flip. The cost estimated by test_mb_mark_used_cost is as following: Before (three runs of test): # test_mb_mark_used_cost: costed jiffies 311 # test_mb_mark_used_cost: costed jiffies 304 # test_mb_mark_used_cost: costed jiffies 305 # test_mb_mark_used_cost: costed jiffies 323 # test_mb_mark_used_cost: costed jiffies 317 # test_mb_mark_used_cost: costed jiffies 317 After (three runs of test): # test_mb_mark_used_cost: costed jiffies 166 # test_mb_mark_used_cost: costed jiffies 152 # test_mb_mark_used_cost: costed jiffies 159 # test_mb_mark_used_cost: costed jiffies 138 # test_mb_mark_used_cost: costed jiffies 149 Signed-off-by: Kemeng Shi --- fs/ext4/mballoc.c | 37 ++++++++++++++++++++----------------- 1 file changed, 20 insertions(+), 17 deletions(-) diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index a61fc52956b2..62d468379722 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -2040,13 +2040,12 @@ static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex) int ord; int mlen = 0; int max = 0; - int cur; int start = ex->fe_start; int len = ex->fe_len; unsigned ret = 0; int len0 = len; void *buddy; - bool split = false; + int ord_start, ord_end; BUG_ON(start + len > (e4b->bd_sb->s_blocksize << 3)); BUG_ON(e4b->bd_group != ex->fe_group); @@ -2071,16 +2070,12 @@ static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex) /* let's maintain buddy itself */ while (len) { - if (!split) - ord = mb_find_order_for_block(e4b, start); + ord = mb_find_order_for_block(e4b, start); if (((start >> ord) << ord) == start && len >= (1 << ord)) { /* the whole chunk may be allocated at once! */ mlen = 1 << ord; - if (!split) - buddy = mb_find_buddy(e4b, ord, &max); - else - split = false; + buddy = mb_find_buddy(e4b, ord, &max); BUG_ON((start >> ord) >= max); mb_set_bit(start >> ord, buddy); e4b->bd_info->bb_counters[ord]--; @@ -2094,20 +2089,28 @@ static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex) if (ret == 0) ret = len | (ord << 16); - /* we have to split large buddy */ BUG_ON(ord <= 0); buddy = mb_find_buddy(e4b, ord, &max); mb_set_bit(start >> ord, buddy); e4b->bd_info->bb_counters[ord]--; - ord--; - cur = (start >> ord) & ~1U; - buddy = mb_find_buddy(e4b, ord, &max); - mb_clear_bit(cur, buddy); - mb_clear_bit(cur + 1, buddy); - e4b->bd_info->bb_counters[ord]++; - e4b->bd_info->bb_counters[ord]++; - split = true; + ord_start = (start >> ord) << ord; + ord_end = ord_start + (1 << ord); + if (start > ord_start) + ext4_mb_mark_free_simple(e4b->bd_sb, e4b->bd_buddy, + ord_start, start - ord_start, + e4b->bd_info); + + if (start + len < ord_end) { + ext4_mb_mark_free_simple(e4b->bd_sb, e4b->bd_buddy, + start + len, + ord_end - (start + len), + e4b->bd_info); + break; + } + + len = start + len - ord_end; + start = ord_end; } mb_set_largest_free_order(e4b->bd_sb, e4b->bd_info);