Re: [PATCH] fs: rotate inodes whose page cache could not be dropped

[Zhihao Cheng]

在 2026/10/16 18:25, Nikolaos Karaolidis 写道:
> When inode_lru_isolate() drops the page cache of an unused inode, it
> has to unlock the list, so it returns LRU_RETRY and the walk restarts
> at the head of the list, where the inode still is. If
> invalidate_mapping_pages() could not empty the mapping, the restarted
> walk strips the same inode again, and so on until nr_to_walk runs out.
> Every walk of that list then ends on this inode, and nothing behind it
> is reclaimed for as long as its cache stays.
[...]
>   static void inode_wait_for_lru_isolating(struct inode *inode)
> @@ -981,7 +980,13 @@ static enum lru_status inode_lru_isolate(struct list_head *item,
>   		else
>   			__count_vm_events(PGINODESTEAL, reap);
>   		mm_account_reclaimed_pages(reap);
> +
> +		spin_lock(&inode->i_lock);
> +		/* The walk restarts here: don't retry leftovers right away */
> +		if (!mapping_empty(&inode->i_data))
> +			inode_state_set(inode, I_REFERENCED);
>   		inode_unpin_lru_isolating(inode);
> +		spin_unlock(&inode->i_lock);
>   		return LRU_RETRY;
>   	}

Hi Nikolaos,
I find a possible BUG_ON if this patch applied, details shown as:
   P1                          P2
prune_icache_sb
 lock(lru->lock)
 inode_lru_isolate
  if (!mapping_empty(&inode->i_data))
   unlock(lru->lock)
   spin_lock(&inode->i_lock)
   inode_state_set(inode, I_REFERENCED)
   inode_unpin_lru_isolating
   spin_unlock(&inode->i_lock)
                         unlink
                          iget_locked // find_inode_fast gets the inode
                          iput
                           iput_final
                            drop = 1
                            evict
                             BUG_ON(inode_state_read_once(inode) != 
(I_FREEING | I_CLEAR))  // inode state with I_REFERENCED

Could that be possible?