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Thu, 25 May 2023 11:33:31 +0000 (GMT) From: Ojaswin Mujoo To: linux-ext4@vger.kernel.org, "Theodore Ts'o" Cc: Ritesh Harjani , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Jan Kara , Kemeng Shi , Ritesh Harjani Subject: [PATCH 10/13] ext4: Ensure ext4_mb_prefetch_fini() is called for all prefetched BGs Date: Thu, 25 May 2023 17:03:04 +0530 Message-Id: X-Mailer: git-send-email 2.31.1 In-Reply-To: References: MIME-Version: 1.0 X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: MhX1_wziKztF6Z7ovYNvKBhCISpLw5hM X-Proofpoint-GUID: hA6Pdv86fDJjuckfV-ZEOD-Nrpg5odjj X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.957,Hydra:6.0.573,FMLib:17.11.176.26 definitions=2023-05-25_06,2023-05-25_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 lowpriorityscore=0 adultscore=0 suspectscore=0 mlxscore=0 malwarescore=0 spamscore=0 bulkscore=0 phishscore=0 impostorscore=0 mlxlogscore=908 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2304280000 definitions=main-2305250096 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Before this patch, the call stack in ext4_run_li_request is as follows: /* * nr = no. of BGs we want to fetch (=s_mb_prefetch) * prefetch_ios = no. of BGs not uptodate after * ext4_read_block_bitmap_nowait() */ next_group = ext4_mb_prefetch(sb, group, nr, prefetch_ios); ext4_mb_prefetch_fini(sb, next_group prefetch_ios); ext4_mb_prefetch_fini() will only try to initialize buddies for BGs in range [next_group - prefetch_ios, next_group). This is incorrect since sometimes (prefetch_ios < nr), which causes ext4_mb_prefetch_fini() to incorrectly ignore some of the BGs that might need initialization. This issue is more notable now with the previous patch enabling "fetching" of BLOCK_UNINIT BGs which are marked buffer_uptodate by default. Fix this by passing nr to ext4_mb_prefetch_fini() instead of prefetch_ios so that it considers the right range of groups. Similarly, make sure we don't pass nr=0 to ext4_mb_prefetch_fini() in ext4_mb_regular_allocator() since we might have prefetched BLOCK_UNINIT groups that would need buddy initialization. Signed-off-by: Ojaswin Mujoo Reviewed-by: Ritesh Harjani (IBM) Reviewed-by: Jan Kara --- fs/ext4/mballoc.c | 4 ---- fs/ext4/super.c | 11 ++++------- 2 files changed, 4 insertions(+), 11 deletions(-) diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c index b35c408cccc2..b6bb314d778e 100644 --- a/fs/ext4/mballoc.c +++ b/fs/ext4/mballoc.c @@ -2732,8 +2732,6 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) if ((prefetch_grp == group) && (cr > CR1 || prefetch_ios < sbi->s_mb_prefetch_limit)) { - unsigned int curr_ios = prefetch_ios; - nr = sbi->s_mb_prefetch; if (ext4_has_feature_flex_bg(sb)) { nr = 1 << sbi->s_log_groups_per_flex; @@ -2742,8 +2740,6 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac) } prefetch_grp = ext4_mb_prefetch(sb, group, nr, &prefetch_ios); - if (prefetch_ios == curr_ios) - nr = 0; } /* This now checks without needing the buddy page */ diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 495f99c10085..37a6fa118ced 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -3694,16 +3694,13 @@ static int ext4_run_li_request(struct ext4_li_request *elr) ext4_group_t group = elr->lr_next_group; unsigned int prefetch_ios = 0; int ret = 0; + int nr = EXT4_SB(sb)->s_mb_prefetch; u64 start_time; if (elr->lr_mode == EXT4_LI_MODE_PREFETCH_BBITMAP) { - elr->lr_next_group = ext4_mb_prefetch(sb, group, - EXT4_SB(sb)->s_mb_prefetch, &prefetch_ios); - if (prefetch_ios) - ext4_mb_prefetch_fini(sb, elr->lr_next_group, - prefetch_ios); - trace_ext4_prefetch_bitmaps(sb, group, elr->lr_next_group, - prefetch_ios); + elr->lr_next_group = ext4_mb_prefetch(sb, group, nr, &prefetch_ios); + ext4_mb_prefetch_fini(sb, elr->lr_next_group, nr); + trace_ext4_prefetch_bitmaps(sb, group, elr->lr_next_group, nr); if (group >= elr->lr_next_group) { ret = 1; if (elr->lr_first_not_zeroed != ngroups &&