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    f2fs: avoid balanc_fs during evict_inode · d4686d56
    Jaegeuk Kim 提交于
    1. Background
    
    Previously, if f2fs tries to move data blocks of an *evicting* inode during the
    cleaning process, it stops the process incompletely and then restarts the whole
    process, since it needs a locked inode to grab victim data pages in its address
    space. In order to get a locked inode, iget_locked() by f2fs_iget() is normally
    used, but, it waits if the inode is on freeing.
    
    So, here is a deadlock scenario.
    1. f2fs_evict_inode()       <- inode "A"
      2. f2fs_balance_fs()
        3. f2fs_gc()
          4. gc_data_segment()
            5. f2fs_iget()      <- inode "A" too!
    
    If step #1 and #5 treat a same inode "A", step #5 would fall into deadlock since
    the inode "A" is on freeing. In order to resolve this, f2fs_iget_nowait() which
    skips __wait_on_freeing_inode() was introduced in step #5, and stops f2fs_gc()
    to complete f2fs_evict_inode().
    
    1. f2fs_evict_inode()           <- inode "A"
      2. f2fs_balance_fs()
        3. f2fs_gc()
          4. gc_data_segment()
            5. f2fs_iget_nowait()   <- inode "A", then stop f2fs_gc() w/ -ENOENT
    
    2. Problem and Solution
    
    In the above scenario, however, f2fs cannot finish f2fs_evict_inode() only if:
     o there are not enough free sections, and
     o f2fs_gc() tries to move data blocks of the *evicting* inode repeatedly.
    
    So, the final solution is to use f2fs_iget() and remove f2fs_balance_fs() in
    f2fs_evict_inode().
    The f2fs_evict_inode() actually truncates all the data and node blocks, which
    means that it doesn't produce any dirty node pages accordingly.
    So, we don't need to do f2fs_balance_fs() in practical.
    Signed-off-by: NJaegeuk Kim <jaegeuk.kim@samsung.com>
    d4686d56
inode.c 7.1 KB