linux-kernel - Re: [PATCH 3/4] mm/readahead: Limit page cache size in page_cache_ra

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Date: Tue, 25 Jun 2024 20:45:26 +0200
From: David Hildenbrand <david@...hat.com>
To: Gavin Shan <gshan@...hat.com>, linux-mm@...ck.org
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 djwong@...nel.org, willy@...radead.org, akpm@...ux-foundation.org,
 hughd@...gle.com, torvalds@...ux-foundation.org, zhenyzha@...hat.com,
 shan.gavin@...il.com
Subject: Re: [PATCH 3/4] mm/readahead: Limit page cache size in
 page_cache_ra_order()

On 25.06.24 11:06, Gavin Shan wrote:
> In page_cache_ra_order(), the maximal order of the page cache to be
> allocated shouldn't be larger than MAX_PAGECACHE_ORDER. Otherwise,
> it's possible the large page cache can't be supported by xarray when
> the corresponding xarray entry is split.
> 
> For example, HPAGE_PMD_ORDER is 13 on ARM64 when the base page size
> is 64KB. The PMD-sized page cache can't be supported by xarray.
> 
> Suggested-by: David Hildenbrand <david@...hat.com>

Heh, you came up with this yourself concurrently :) so feel free to drop 
that.

Acked-by: David Hildenbrand <david@...hat.com>

> Signed-off-by: Gavin Shan <gshan@...hat.com>
> ---
>   mm/readahead.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/readahead.c b/mm/readahead.c
> index c1b23989d9ca..817b2a352d78 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -503,11 +503,11 @@ void page_cache_ra_order(struct readahead_control *ractl,
>   
>   	limit = min(limit, index + ra->size - 1);
>   
> -	if (new_order < MAX_PAGECACHE_ORDER) {
> +	if (new_order < MAX_PAGECACHE_ORDER)
>   		new_order += 2;
> -		new_order = min_t(unsigned int, MAX_PAGECACHE_ORDER, new_order);
> -		new_order = min_t(unsigned int, new_order, ilog2(ra->size));
> -	}
> +
> +	new_order = min_t(unsigned int, MAX_PAGECACHE_ORDER, new_order);
> +	new_order = min_t(unsigned int, new_order, ilog2(ra->size));
>   
>   	/* See comment in page_cache_ra_unbounded() */
>   	nofs = memalloc_nofs_save();

-- 
Cheers,

David / dhildenb