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@redhat.com>
Signed-off-by: Gavin Shan <gshan@redhat.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();
-- 
2.45.1

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@redhat.com>

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

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

> Signed-off-by: Gavin Shan <gshan@redhat.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

On 6/26/24 4:45 AM, David Hildenbrand wrote:
> 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@redhat.com>
> 
> Heh, you came up with this yourself concurrently :) so feel free to drop that.
> 
> Acked-by: David Hildenbrand <david@redhat.com>
> 

David, thanks for your follow-up and reviews. I will drop that tag in next respin :)

Thanks,
Gavin

>> Signed-off-by: Gavin Shan <gshan@redhat.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();
>