Re: [PATCH RFC] mm/readahead: Fix repeat initial_readahead

[Jan Kara]

On Tue 25-06-24 14:28:34, zippermonkey wrote:
> To illustrate this problem, I created the following example:
> 
> Assuming that the process reads sequentially from the beginning of the file
> and
> calls the `page_cache_sync_readahead` function. In this sync readahead
> function,
> since the index is 0, it will proceed to `initial_readahead` and initialize
> `ra_state`. It allocates a folio with an order of 2 and marks it as
> PG_readahead.
> Next, because` (folio_test_readahead(folio))` is true, the
> page_cache_async_ra
> function is called, which causes the `ra_state` to be initialized again.

Good spotting guys! There are actually more problems in the readahead code.
I have just pushed out a patch series [1] addressing several issues that
should also address the problem you've found. Can you please test whether
it provides a similar speedup as your fix (sorry, I forgot to CC you on the
series)? Thanks!

[1] https://lore.kernel.org/20240625100859.15507-1-jack@xxxxxxx

								Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR