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Date: Mon, 30 Jul 2018 14:36:19 +0800
From: Chao Yu <yuchao0@...wei.com>
To: Jaegeuk Kim <jaegeuk@...nel.org>
CC: <linux-kernel@...r.kernel.org>,
<linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [PATCH] f2fs: avoid fi->i_gc_rwsem[WRITE] lock in f2fs_gc
On 2018/7/30 12:18, Jaegeuk Kim wrote:
> On 07/30, Chao Yu wrote:
>> On 2018/7/30 9:32, Jaegeuk Kim wrote:
>>> The f2fs_gc() called by f2fs_balance_fs() requires to be called outside of
>>> fi->i_gc_rwsem[WRITE], since f2fs_gc() can try to grab it in a loop.
>>>
>>> If it hits the miximum retrials in GC, let's give a chance to release
>>> gc_mutex for a short time in order not to go into live lock in the worst
>>> case.
>>>
>>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
>>> ---
>>> fs/f2fs/f2fs.h | 1 +
>>> fs/f2fs/file.c | 62 ++++++++++++++++++++++-------------------------
>>> fs/f2fs/gc.c | 22 ++++++++++++-----
>>> fs/f2fs/segment.c | 5 +++-
>>> fs/f2fs/segment.h | 2 +-
>>> 5 files changed, 51 insertions(+), 41 deletions(-)
>>>
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index a9447c7d6570..50349780001b 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -1223,6 +1223,7 @@ struct f2fs_sb_info {
>>> unsigned int gc_mode; /* current GC state */
>>> /* for skip statistic */
>>> unsigned long long skipped_atomic_files[2]; /* FG_GC and BG_GC */
>>> + unsigned long long skipped_gc_rwsem; /* FG_GC only */
>>>
>>> /* threshold for gc trials on pinned files */
>>> u64 gc_pin_file_threshold;
>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>> index 78c1bd6b8497..2b7d26ebb294 100644
>>> --- a/fs/f2fs/file.c
>>> +++ b/fs/f2fs/file.c
>>> @@ -1179,10 +1179,12 @@ static int __exchange_data_block(struct inode *src_inode,
>>> return ret;
>>> }
>>>
>>> -static int f2fs_do_collapse(struct inode *inode, pgoff_t start, pgoff_t end)
>>> +static int f2fs_do_collapse(struct inode *inode, loff_t offset, loff_t len)
>>> {
>>> struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>>> pgoff_t nrpages = (i_size_read(inode) + PAGE_SIZE - 1) / PAGE_SIZE;
>>> + pgoff_t start = offset >> PAGE_SHIFT;
>>> + pgoff_t end = (offset + len) >> PAGE_SHIFT;
>>> int ret;
>>>
>>> f2fs_balance_fs(sbi, true);
>>> @@ -1190,14 +1192,18 @@ static int f2fs_do_collapse(struct inode *inode, pgoff_t start, pgoff_t end)
>>>
>>> f2fs_drop_extent_tree(inode);
>>>
>>> + /* avoid gc operation during block exchange */
>>> + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>> + truncate_pagecache(inode, offset);
>>> ret = __exchange_data_block(inode, inode, end, start, nrpages - end, true);
>>> + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>> +
>>> f2fs_unlock_op(sbi);
>>> return ret;
>>> }
>>>
>>> static int f2fs_collapse_range(struct inode *inode, loff_t offset, loff_t len)
>>> {
>>> - pgoff_t pg_start, pg_end;
>>> loff_t new_size;
>>> int ret;
>>>
>>> @@ -1212,21 +1218,13 @@ static int f2fs_collapse_range(struct inode *inode, loff_t offset, loff_t len)
>>> if (ret)
>>> return ret;
>>>
>>> - pg_start = offset >> PAGE_SHIFT;
>>> - pg_end = (offset + len) >> PAGE_SHIFT;
>>> -
>>> - /* avoid gc operation during block exchange */
>>> - down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>> -
>>> down_write(&F2FS_I(inode)->i_mmap_sem);
>>> /* write out all dirty pages from offset */
>>> ret = filemap_write_and_wait_range(inode->i_mapping, offset, LLONG_MAX);
>>> if (ret)
>>> goto out_unlock;
>>>
>>> - truncate_pagecache(inode, offset);
>>> -
>>> - ret = f2fs_do_collapse(inode, pg_start, pg_end);
>>> + ret = f2fs_do_collapse(inode, offset, len);
>>> if (ret)
>>> goto out_unlock;
>>>
>>> @@ -1242,7 +1240,6 @@ static int f2fs_collapse_range(struct inode *inode, loff_t offset, loff_t len)
>>> f2fs_i_size_write(inode, new_size);
>>> out_unlock:
>>> up_write(&F2FS_I(inode)->i_mmap_sem);
>>> - up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>> return ret;
>>> }
>>>
>>> @@ -1417,9 +1414,6 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
>>>
>>> f2fs_balance_fs(sbi, true);
>>>
>>> - /* avoid gc operation during block exchange */
>>> - down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>> -
>>> down_write(&F2FS_I(inode)->i_mmap_sem);
>>> ret = f2fs_truncate_blocks(inode, i_size_read(inode), true);
>>> if (ret)
>>> @@ -1430,13 +1424,15 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
>>> if (ret)
>>> goto out;
>>>
>>> - truncate_pagecache(inode, offset);
>>> -
>>> pg_start = offset >> PAGE_SHIFT;
>>> pg_end = (offset + len) >> PAGE_SHIFT;
>>> delta = pg_end - pg_start;
>>> idx = (i_size_read(inode) + PAGE_SIZE - 1) / PAGE_SIZE;
>>>
>>> + /* avoid gc operation during block exchange */
>>> + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>> + truncate_pagecache(inode, offset);
>>> +
>>> while (!ret && idx > pg_start) {
>>> nr = idx - pg_start;
>>> if (nr > delta)
>>> @@ -1450,6 +1446,7 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
>>> idx + delta, nr, false);
>>> f2fs_unlock_op(sbi);
>>> }
>>> + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>
>>> /* write out all moved pages, if possible */
>>> filemap_write_and_wait_range(inode->i_mapping, offset, LLONG_MAX);
>>> @@ -1459,7 +1456,6 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
>>> f2fs_i_size_write(inode, new_size);
>>> out:
>>> up_write(&F2FS_I(inode)->i_mmap_sem);
>>> - up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>> return ret;
>>> }
>>>
>>> @@ -1706,8 +1702,6 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>>>
>>> inode_lock(inode);
>>>
>>> - down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>
>> After removing lock here, how can we handle below condition:
>>
>> commit 27319ba4044c0c67d62ae39e53c0118c89f0a029
>> Author: Chao Yu <yuchao0@...wei.com>
>> Date: Tue Apr 17 17:51:28 2018 +0800
>>
>> f2fs: fix race in between GC and atomic open
>>
>> Thread GC thread
>> - f2fs_ioc_start_atomic_write
>> - get_dirty_pages
>> - filemap_write_and_wait_range
>> - f2fs_gc
>> - do_garbage_collect
>> - gc_data_segment
>> - move_data_page
>> - f2fs_is_atomic_file
>> - set_page_dirty
>> - set_inode_flag(, FI_ATOMIC_FILE)
>>
>> Dirty data page can still be generated by GC in race condition as
>> above call stack.
>>
>> This patch adds fi->dio_rwsem[WRITE] in f2fs_ioc_start_atomic_write
>> to avoid such race.
>
> "f2fs: don't allow any writes on aborted atomic writes" disallows any writes
> on atomic file which has the revoking flag. So, this won't happen. In GC,
Hmmm... In above condition, it's not related to FI_ATOMIC_REVOKE_REQUEST flag
since we do not drop any inmem pages for atomic file.
That patch was trying to eliminate a hole which exists in between
filemap_write_and_wait_range and set_inode_flag(, FI_ATOMIC_FILE), where GC can
still dirty page in the inode, it can pollute isolation of database transaction,
so that is why we need this lock.
Thanks,
> f2fs_is_atomic_file won't make the page dirty. WDYT?
>
> Thanks,
>
>
>>
>> Thanks,
>>
>>> -
>>> if (f2fs_is_atomic_file(inode)) {
>>> if (is_inode_flag_set(inode, FI_ATOMIC_REVOKE_REQUEST))
>>> ret = -EINVAL;
>>> @@ -1736,7 +1730,6 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
>>> stat_inc_atomic_write(inode);
>>> stat_update_max_atomic_write(inode);
>>> out:
>>> - up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>> inode_unlock(inode);
>>> mnt_drop_write_file(filp);
>>> return ret;
>>> @@ -1754,9 +1747,9 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
>>> if (ret)
>>> return ret;
>>>
>>> - inode_lock(inode);
>>> + f2fs_balance_fs(F2FS_I_SB(inode), true);
>>>
>>> - down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>> + inode_lock(inode);
>>>
>>> if (f2fs_is_volatile_file(inode)) {
>>> ret = -EINVAL;
>>> @@ -1782,7 +1775,6 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
>>> clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
>>> ret = -EINVAL;
>>> }
>>> - up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>> inode_unlock(inode);
>>> mnt_drop_write_file(filp);
>>> return ret;
>>> @@ -2378,15 +2370,10 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
>>> }
>>>
>>> inode_lock(src);
>>> - down_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
>>> if (src != dst) {
>>> ret = -EBUSY;
>>> if (!inode_trylock(dst))
>>> goto out;
>>> - if (!down_write_trylock(&F2FS_I(dst)->i_gc_rwsem[WRITE])) {
>>> - inode_unlock(dst);
>>> - goto out;
>>> - }
>>> }
>>>
>>> ret = -EINVAL;
>>> @@ -2432,6 +2419,14 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
>>>
>>> f2fs_balance_fs(sbi, true);
>>> f2fs_lock_op(sbi);
>>> +
>>> + down_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
>>> + if (src != dst) {
>>> + ret = -EBUSY;
>>> + if (!down_write_trylock(&F2FS_I(dst)->i_gc_rwsem[WRITE]))
>>> + goto out_src;
>>> + }
>>> +
>>> ret = __exchange_data_block(src, dst, pos_in >> F2FS_BLKSIZE_BITS,
>>> pos_out >> F2FS_BLKSIZE_BITS,
>>> len >> F2FS_BLKSIZE_BITS, false);
>>> @@ -2442,14 +2437,15 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
>>> else if (dst_osize != dst->i_size)
>>> f2fs_i_size_write(dst, dst_osize);
>>> }
>>> + if (src != dst)
>>> + up_write(&F2FS_I(dst)->i_gc_rwsem[WRITE]);
>>> +out_src:
>>> + up_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
>>> f2fs_unlock_op(sbi);
>>> out_unlock:
>>> - if (src != dst) {
>>> - up_write(&F2FS_I(dst)->i_gc_rwsem[WRITE]);
>>> + if (src != dst)
>>> inode_unlock(dst);
>>> - }
>>> out:
>>> - up_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
>>> inode_unlock(src);
>>> return ret;
>>> }
>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>> index e352fbd33848..cac317e37306 100644
>>> --- a/fs/f2fs/gc.c
>>> +++ b/fs/f2fs/gc.c
>>> @@ -884,6 +884,7 @@ static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
>>> if (!down_write_trylock(
>>> &F2FS_I(inode)->i_gc_rwsem[WRITE])) {
>>> iput(inode);
>>> + sbi->skipped_gc_rwsem++;
>>> continue;
>>> }
>>>
>>> @@ -913,6 +914,7 @@ static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
>>> continue;
>>> if (!down_write_trylock(
>>> &fi->i_gc_rwsem[WRITE])) {
>>> + sbi->skipped_gc_rwsem++;
>>> up_write(&fi->i_gc_rwsem[READ]);
>>> continue;
>>> }
>>> @@ -1062,6 +1064,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
>>> prefree_segments(sbi));
>>>
>>> cpc.reason = __get_cp_reason(sbi);
>>> + sbi->skipped_gc_rwsem = 0;
>>> gc_more:
>>> if (unlikely(!(sbi->sb->s_flags & SB_ACTIVE))) {
>>> ret = -EINVAL;
>>> @@ -1103,7 +1106,8 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
>>> total_freed += seg_freed;
>>>
>>> if (gc_type == FG_GC) {
>>> - if (sbi->skipped_atomic_files[FG_GC] > last_skipped)
>>> + if (sbi->skipped_atomic_files[FG_GC] > last_skipped ||
>>> + sbi->skipped_gc_rwsem)
>>> skipped_round++;
>>> last_skipped = sbi->skipped_atomic_files[FG_GC];
>>> round++;
>>> @@ -1112,15 +1116,21 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
>>> if (gc_type == FG_GC)
>>> sbi->cur_victim_sec = NULL_SEGNO;
>>>
>>> - if (!sync) {
>>> - if (has_not_enough_free_secs(sbi, sec_freed, 0)) {
>>> - if (skipped_round > MAX_SKIP_ATOMIC_COUNT &&
>>> - skipped_round * 2 >= round)
>>> - f2fs_drop_inmem_pages_all(sbi, true);
>>> + if (sync)
>>> + goto stop;
>>> +
>>> + if (has_not_enough_free_secs(sbi, sec_freed, 0)) {
>>> + if (skipped_round <= MAX_SKIP_GC_COUNT ||
>>> + skipped_round * 2 < round) {
>>> segno = NULL_SEGNO;
>>> goto gc_more;
>>> }
>>>
>>> + if (sbi->skipped_atomic_files[FG_GC] == last_skipped) {
>>> + f2fs_drop_inmem_pages_all(sbi, true);
>>> + segno = NULL_SEGNO;
>>> + goto gc_more;
>>> + }
>>> if (gc_type == FG_GC)
>>> ret = f2fs_write_checkpoint(sbi, &cpc);
>>> }
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index 3662e1f429b4..15b3b095fd58 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -444,10 +444,12 @@ int f2fs_commit_inmem_pages(struct inode *inode)
>>> struct f2fs_inode_info *fi = F2FS_I(inode);
>>> int err;
>>>
>>> - f2fs_balance_fs(sbi, true);
>>> + f2fs_balance_fs(F2FS_I_SB(inode), true);
>>> +
>>> f2fs_lock_op(sbi);
>>>
>>> set_inode_flag(inode, FI_ATOMIC_COMMIT);
>>> + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>
>>> mutex_lock(&fi->inmem_lock);
>>> err = __f2fs_commit_inmem_pages(inode);
>>> @@ -458,6 +460,7 @@ int f2fs_commit_inmem_pages(struct inode *inode)
>>> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>>> mutex_unlock(&fi->inmem_lock);
>>>
>>> + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>> clear_inode_flag(inode, FI_ATOMIC_COMMIT);
>>>
>>> f2fs_unlock_op(sbi);
>>> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
>>> index 50495515f0a0..b3d9e317ff0c 100644
>>> --- a/fs/f2fs/segment.h
>>> +++ b/fs/f2fs/segment.h
>>> @@ -215,7 +215,7 @@ struct segment_allocation {
>>> #define IS_DUMMY_WRITTEN_PAGE(page) \
>>> (page_private(page) == (unsigned long)DUMMY_WRITTEN_PAGE)
>>>
>>> -#define MAX_SKIP_ATOMIC_COUNT 16
>>> +#define MAX_SKIP_GC_COUNT 16
>>>
>>> struct inmem_pages {
>>> struct list_head list;
>>>
>
> .
>
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