linux-kernel - Re: [PATCH RFC] mm/readahead: Fix repeat initial

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Date: Tue, 25 Jun 2024 14:28:34 +0800
From: zippermonkey <zzippermonkey@...look.com>
To: zhangpengpeng0808@...il.com
Cc: akpm@...ux-foundation.org, bruzzhang@...cent.com,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, vernhao@...cent.com, willy@...radead.org,
 zigiwang@...cent.com, jack@...e.cz
Subject: Re: [PATCH RFC] mm/readahead: Fix repeat initial_readahead

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.