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

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Date: Wed, 26 Jun 2024 10:48:52 +1000
From: Gavin Shan <gshan@...hat.com>
To: David Hildenbrand <david@...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 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@...hat.com>
> 
> Heh, you came up with this yourself concurrently :) so feel free to drop that.
> 
> Acked-by: David Hildenbrand <david@...hat.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@...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();
>