On Tue, Nov 24, 2015 at 09:47:31AM +0100, Jan Kara wrote:
> Ted and Namjae have reported that truncated pages don't get timely
> reclaimed after being truncated in data=journal mode. The following test
> triggers the issue easily:
>
> for (i = 0; i < 1000; i++) {
> pwrite(fd, buf, 1024*1024, 0);
> fsync(fd);
> fsync(fd);
> ftruncate(fd, 0);
> }
>
> The reason is that journal_unmap_buffer() finds that truncated buffers
> are not journalled (jh->b_transaction == NULL), they are part of
> checkpoint list of a transaction (jh->b_cp_transaction != NULL) and have
> been already written out (!buffer_dirty(bh)). We clean such buffers but
> we leave them in the checkpoint list. Since checkpoint transaction holds
> a reference to the journal head, these buffers cannot be released until
> the checkpoint transaction is cleaned up. And at that point we don't
> call release_buffer_page() anymore so pages detached from mapping are
> lingering in the system waiting for reclaim to find them and free them.
>
> Fix the problem by removing buffers from transaction checkpoint lists
> when journal_unmap_buffer() finds out they don't have to be there
> anymore.
>
> Reported-and-tested-by: Namjae Jeon <namjae.jeon@xxxxxxxxxxx>
> Fixes: de1b794130b130e77ffa975bb58cb843744f9ae5
> Signed-off-by: Jan Kara <jack@xxxxxxx>
Thanks, applied. Many thanks to Namjae and Jan for tracking this down!!
- Ted
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