[f2fs-dev] 答复: [PATCH v2 1/2] f2fs: fix to shrink read extent node in batches

Commit Message

王秀红 (Xiuhong Wang) Nov. 25, 2024, 3:11 a.m. UTC

Hi Chao,

after tested in this weekend with these patch base on the orginal case, no issue reproduced, so
Tested-by: Xiuhong Wang <[e-mail]>

thanks!

-----邮件原件-----
发件人: Chao Yu <[e-mail]> 
发送时间: 2024年11月22日 14:50
收件人: [e-mail]
抄送: [e-mail]; [e-mail]; Chao Yu <[e-mail]>; 王秀红 (Xiuhong Wang) <[e-mail]>; 牛志国 (Zhiguo Niu) <[e-mail]>
主题: [PATCH v2 1/2] f2fs: fix to shrink read extent node in batches


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We use rwlock to protect core structure data of extent tree during its shrink, however, if there is a huge number of extent nodes in extent tree, during shrink of extent tree, it may hold rwlock for a very long time, which may trigger kernel hang issue.

This patch fixes to shrink read extent node in batches, so that, critical region of the rwlock can be shrunk to avoid its extreme long time hold.

Reported-by: Xiuhong Wang <[e-mail]>
Closes: https://lore.kernel.org/linux-f2fs-devel/[e-mail]/
Signed-off-by: Xiuhong Wang <[e-mail]>
Signed-off-by: Zhiguo Niu <[e-mail]>
Signed-off-by: Chao Yu <[e-mail]>
---
v2:
- no updates.
 fs/f2fs/extent_cache.c | 69 +++++++++++++++++++++++++-----------------
 1 file changed, 41 insertions(+), 28 deletions(-)

 }

+static unsigned int __destroy_extent_node(struct inode *inode,
+                                       enum extent_type type) {
+       struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
+       struct extent_tree *et = F2FS_I(inode)->extent_tree[type];
+       unsigned int nr_shrink = type == EX_READ ?
+                               READ_EXTENT_CACHE_SHRINK_NUMBER :
+                               AGE_EXTENT_CACHE_SHRINK_NUMBER;
+       unsigned int node_cnt = 0;
+
+       if (!et || !atomic_read(&et->node_cnt))
+               return 0;
+
+       while (atomic_read(&et->node_cnt)) {
+               write_lock(&et->lock);
+               node_cnt += __free_extent_tree(sbi, et, nr_shrink);
+               write_unlock(&et->lock);
+       }
+
+       f2fs_bug_on(sbi, atomic_read(&et->node_cnt));
+
+       return node_cnt;
+}
+
 static void __update_extent_tree_range(struct inode *inode,
                        struct extent_info *tei, enum extent_type type)  { @@ -760,9 +785,6 @@ static void __update_extent_tree_range(struct inode *inode,
                }
        }

-       if (is_inode_flag_set(inode, FI_NO_EXTENT))
-               __free_extent_tree(sbi, et);
-
        if (et->largest_updated) {
                et->largest_updated = false;
                updated = true;
@@ -780,6 +802,9 @@ static void __update_extent_tree_range(struct inode *inode,
 out_read_extent_cache:
        write_unlock(&et->lock);

+       if (is_inode_flag_set(inode, FI_NO_EXTENT))
+               __destroy_extent_node(inode, EX_READ);
+
        if (updated)
                f2fs_mark_inode_dirty_sync(inode, true);  } @@ -942,10 +967,14 @@ static unsigned int __shrink_extent_tree(struct f2fs_sb_info *sbi, int nr_shrink
        list_for_each_entry_safe(et, next, &eti->zombie_list, list) {
                if (atomic_read(&et->node_cnt)) {
                        write_lock(&et->lock);
-                       node_cnt += __free_extent_tree(sbi, et);
+                       node_cnt += __free_extent_tree(sbi, et,
+                                       nr_shrink - node_cnt - 
+ tree_cnt);
                        write_unlock(&et->lock);
                }
-               f2fs_bug_on(sbi, atomic_read(&et->node_cnt));
+
+               if (atomic_read(&et->node_cnt))
+                       goto unlock_out;
+
                list_del_init(&et->list);
                radix_tree_delete(&eti->extent_tree_root, et->ino);
                kmem_cache_free(extent_tree_slab, et); @@ -1084,23 +1113,6 @@ unsigned int f2fs_shrink_age_extent_tree(struct f2fs_sb_info *sbi, int nr_shrink
        return __shrink_extent_tree(sbi, nr_shrink, EX_BLOCK_AGE);  }

-static unsigned int __destroy_extent_node(struct inode *inode,
-                                       enum extent_type type)
-{
-       struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
-       struct extent_tree *et = F2FS_I(inode)->extent_tree[type];
-       unsigned int node_cnt = 0;
-
-       if (!et || !atomic_read(&et->node_cnt))
-               return 0;
-
-       write_lock(&et->lock);
-       node_cnt = __free_extent_tree(sbi, et);
-       write_unlock(&et->lock);
-
-       return node_cnt;
-}
-
 void f2fs_destroy_extent_node(struct inode *inode)  {
        __destroy_extent_node(inode, EX_READ); @@ -1109,7 +1121,6 @@ void f2fs_destroy_extent_node(struct inode *inode)

 static void __drop_extent_tree(struct inode *inode, enum extent_type type)  {
-       struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
        struct extent_tree *et = F2FS_I(inode)->extent_tree[type];
        bool updated = false;

@@ -1117,7 +1128,6 @@ static void __drop_extent_tree(struct inode *inode, enum extent_type type)
                return;

        write_lock(&et->lock);
-       __free_extent_tree(sbi, et);
        if (type == EX_READ) {
                set_inode_flag(inode, FI_NO_EXTENT);
                if (et->largest.len) {
@@ -1126,6 +1136,9 @@ static void __drop_extent_tree(struct inode *inode, enum extent_type type)
                }
        }
        write_unlock(&et->lock);
+
+       __destroy_extent_node(inode, type);
+
        if (updated)
                f2fs_mark_inode_dirty_sync(inode, true);  }
--
2.40.1

Patch

diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c index 019c1f7b7fa5..b7a6817b44b0 100644
--- a/fs/f2fs/extent_cache.c
+++ b/fs/f2fs/extent_cache.c
@@ -379,21 +379,22 @@  static struct extent_tree *__grab_extent_tree(struct inode *inode,  }

 static unsigned int __free_extent_tree(struct f2fs_sb_info *sbi,
-                                       struct extent_tree *et)
+                               struct extent_tree *et, unsigned int 
+ nr_shrink)
 {
        struct rb_node *node, *next;
        struct extent_node *en;
-       unsigned int count = atomic_read(&et->node_cnt);
+       unsigned int count;

        node = rb_first_cached(&et->root);
-       while (node) {
+
+       for (count = 0; node && count < nr_shrink; count++) {
                next = rb_next(node);
                en = rb_entry(node, struct extent_node, rb_node);
                __release_extent_node(sbi, et, en);
                node = next;
        }

-       return count - atomic_read(&et->node_cnt);
+       return count;
 }

 static void __drop_largest_extent(struct extent_tree *et, @@ -622,6 +623,30 @@ static struct extent_node *__insert_extent_tree(struct f2fs_sb_info *sbi,
        return en;