linux-kernel - Re: [PATCH] mm/shmem: Do not wait for lock_page() in shmem_unused_huge

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Message-ID: <20180316133417.hk2lvnvgildsc65n@node.shutemov.name>
Date:   Fri, 16 Mar 2018 16:34:17 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     mhocko@...nel.org, kirill.shutemov@...ux.intel.com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux-mm@...ts.ewheeler.net
Subject: Re: [PATCH] mm/shmem: Do not wait for lock_page() in
 shmem_unused_huge_shrink()

On Fri, Mar 16, 2018 at 10:14:24PM +0900, Tetsuo Handa wrote:
> f2fs is doing
> 
>   page = f2fs_pagecache_get_page(inode->i_mapping, 0, FGP_LOCK|FGP_NOWAIT, 0);
> 
> which calls
> 
>   struct page *pagecache_get_page(inode->i_mapping, 0, FGP_LOCK|FGP_NOWAIT, 0);
> 
> . Then, can't we define
> 
>   static inline struct page *find_trylock_page(struct address_space *mapping,
>   					     pgoff_t offset)
>   {
>   	return pagecache_get_page(mapping, offset, FGP_LOCK|FGP_NOWAIT, 0);
>   }
> 
> and replace find_lock_page() with find_trylock_page() ?

This won't work in this case. We need to destinct no-page-in-page-cache
from failed-to-lock-page. We take different routes depending on this.

-- 
 Kirill A. Shutemov