From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga05-in.huawei.com (szxga05-in.huawei.com [45.249.212.191]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0706311CA0; Sat, 19 Jul 2025 01:37:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.191 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752889050; cv=none; b=a796FUbb0/J0sW59Z3Td2a9q/HxQAYStA6d0UISytbtP/H3POpg129uXrRES+8Md+Wp2xiw9xMEk+Rb2gdrX/DhoEjf7C3p4l1KikooYxhBNSWLGW0lAJT5JmJNpxVMwuETSdIxXStvsLb94pA9zv/n+covujDul4X9YSvFz8CU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752889050; c=relaxed/simple; bh=qUWcvyRchuCny4BQeqUugOJr2SgYl3yTQxte0+P8zJA=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=ewUUhU7Kjj1eSMlsD+NCQm2MXrE/878Qt8UdsSXc45vcKY29O8ya5U/NkyRoehmbL9h4mNQjLT0tf5xA+RCsLp+vYuNJjYxp0NQjcbZRdB8uf2NDllVJvnimNRlWUBS+J10bCyblzUdoM6nGbh+9tsHEPUbIGdZ8GPlp9ra/Hmg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.191 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.88.234]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4bkTjX0fXbz2gKf1; Sat, 19 Jul 2025 09:34:40 +0800 (CST) Received: from dggpemf500013.china.huawei.com (unknown [7.185.36.188]) by mail.maildlp.com (Postfix) with ESMTPS id A04E1140295; Sat, 19 Jul 2025 09:37:18 +0800 (CST) Received: from [127.0.0.1] (10.174.177.71) by dggpemf500013.china.huawei.com (7.185.36.188) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.11; Sat, 19 Jul 2025 09:37:17 +0800 Message-ID: Date: Sat, 19 Jul 2025 09:37:16 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 02/17] ext4: separate stream goal hits from s_bal_goals for better tracking To: Ojaswin Mujoo CC: , , , , , , , , References: <20250714130327.1830534-1-libaokun1@huawei.com> <20250714130327.1830534-3-libaokun1@huawei.com> Content-Language: en-US From: Baokun Li In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: kwepems500001.china.huawei.com (7.221.188.70) To dggpemf500013.china.huawei.com (7.185.36.188) On 2025/7/17 18:29, Ojaswin Mujoo wrote: > On Mon, Jul 14, 2025 at 09:03:12PM +0800, Baokun Li wrote: >> In ext4_mb_regular_allocator(), after the call to ext4_mb_find_by_goal() >> fails to achieve the inode goal, allocation continues with the stream >> allocation global goal. Currently, hits for both are combined in >> sbi->s_bal_goals, hindering accurate optimization. >> >> This commit separates global goal hits into sbi->s_bal_stream_goals. Since >> stream allocation doesn't use ac->ac_g_ex.fe_start, set fe_start to -1. >> This prevents stream allocations from being counted in s_bal_goals. Also >> clear EXT4_MB_HINT_TRY_GOAL to avoid calling ext4_mb_find_by_goal again. >> >> After adding `stream_goal_hits`, `/proc/fs/ext4/sdx/mb_stats` will show: >> >> mballoc: >> reqs: 840347 >> success: 750992 >> groups_scanned: 1230506 >> cr_p2_aligned_stats: >> hits: 21531 >> groups_considered: 411664 >> extents_scanned: 21531 >> useless_loops: 0 >> bad_suggestions: 6 >> cr_goal_fast_stats: >> hits: 111222 >> groups_considered: 1806728 >> extents_scanned: 467908 >> useless_loops: 0 >> bad_suggestions: 13 >> cr_best_avail_stats: >> hits: 36267 >> groups_considered: 1817631 >> extents_scanned: 156143 >> useless_loops: 0 >> bad_suggestions: 204 >> cr_goal_slow_stats: >> hits: 106396 >> groups_considered: 5671710 >> extents_scanned: 22540056 >> useless_loops: 123747 >> cr_any_free_stats: >> hits: 138071 >> groups_considered: 724692 >> extents_scanned: 23615593 >> useless_loops: 585 >> extents_scanned: 46804261 >> goal_hits: 1307 >> stream_goal_hits: 236317 >> len_goal_hits: 155549 >> 2^n_hits: 21531 >> breaks: 225096 >> lost: 35062 >> buddies_generated: 40/40 >> buddies_time_used: 48004 >> preallocated: 5962467 >> discarded: 4847560 >> >> Signed-off-by: Baokun Li >> --- >> fs/ext4/ext4.h | 1 + >> fs/ext4/mballoc.c | 11 +++++++++-- >> 2 files changed, 10 insertions(+), 2 deletions(-) >> >> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h >> index 9df74123e7e6..8750ace12935 100644 >> --- a/fs/ext4/ext4.h >> +++ b/fs/ext4/ext4.h >> @@ -1646,6 +1646,7 @@ struct ext4_sb_info { >> atomic_t s_bal_cX_ex_scanned[EXT4_MB_NUM_CRS]; /* total extents scanned */ >> atomic_t s_bal_groups_scanned; /* number of groups scanned */ >> atomic_t s_bal_goals; /* goal hits */ >> + atomic_t s_bal_stream_goals; /* stream allocation global goal hits */ >> atomic_t s_bal_len_goals; /* len goal hits */ >> atomic_t s_bal_breaks; /* too long searches */ >> atomic_t s_bal_2orders; /* 2^order hits */ >> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c >> index 336d65c4f6a2..f56ac477c464 100644 >> --- a/fs/ext4/mballoc.c >> +++ b/fs/ext4/mballoc.c >> @@ -2849,8 +2849,9 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) >> /* TBD: may be hot point */ >> spin_lock(&sbi->s_md_lock); >> ac->ac_g_ex.fe_group = sbi->s_mb_last_group; >> - ac->ac_g_ex.fe_start = sbi->s_mb_last_start; >> spin_unlock(&sbi->s_md_lock); >> + ac->ac_g_ex.fe_start = -1; >> + ac->ac_flags &= ~EXT4_MB_HINT_TRY_GOAL; > Hey Baokun, I was a bit late to review this in v2 so I'll add the > comment here: > > So this is mostly to account for retires right? Maybe rather than > disabling goal allocation a better way to do this is resetting the > original goal group and goal start in the retry logic of > ext4_mb_new_blocks()? Since we drop preallocations before retrying, this > way we might actually find our goal during the retry. Its a slim chance > though but still feels like the right way to do it. > > Thoughts? It's true that successfully acquiring the goal on retry is possible, but the probability is too low; I think attempting the inode goal on retry is not very meaningful. The lack of trylock logic in ext4_mb_find_by_goal() also introduces some performance overhead. Additionally, since preallocations might be dropped before retrying, the inode's preallocation could also be discarded. Therefore, pa overlap needs to be re-adjusted. For data block allocation, we should call ext4_mb_normalize_request() to regenerate a new ac_g_ex instead of directly resetting the original goal. ext4_mb_normalize_request() will also determine whether to reset EXT4_MB_HINT_TRY_GOAL. For metadata block allocation, EXT4_MB_STREAM_ALLOC is not set, so there's no need to worry about EXT4_MB_HINT_TRY_GOAL being cleared. Clearing EXT4_MB_HINT_TRY_GOAL here is only to avoid inode goal allocation with -1. If you insist that we should attempt the inode goal on retry, I will send a separate patch to address that. Cheers, Baokun