Re: [PATCH v2 5/7] btrfs: convert heuristic_collect_sample() to use folios

[Tal Zussman]

On 9/9/26 4:26 AM, David Sterba wrote:
> On Mon, Sep 07, 2026 at 04:19:59PM -0400, Tal Zussman wrote:
>> Convert the sampling loop to folios. This removes the last caller of
>> find_get_page() in btrfs and saves a call to compound_head() per sampled
>> page. Document that the lookup is not supposed to fail with an ASSERT().
>> 
>> Reviewed-by: Qu Wenruo <wqu@xxxxxxxx>
>> Signed-off-by: Tal Zussman <tz2294@xxxxxxxxxxxx>
>> ---
>>  fs/btrfs/compression.c | 10 ++++++----
>>  1 file changed, 6 insertions(+), 4 deletions(-)
>> 
>> diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
>> index 979b2ffbd8fc..fa8b92592321 100644
>> --- a/fs/btrfs/compression.c
>> +++ b/fs/btrfs/compression.c
>> @@ -1488,7 +1488,7 @@ static bool sample_repeated_patterns(struct heuristic_ws *ws)
>>  static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end,
>>  				     struct heuristic_ws *ws)
>>  {
>> -	struct page *page;
>> +	struct folio *folio;
>>  	pgoff_t index, index_end;
>>  	u32 i, curr_sample_pos;
>>  	u8 *in_data;
>> @@ -1514,8 +1514,10 @@ static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end,
>>  
>>  	curr_sample_pos = 0;
>>  	while (index < index_end) {
>> -		page = find_get_page(inode->i_mapping, index);
>> -		in_data = kmap_local_page(page);
>> +		folio = filemap_get_folio(inode->i_mapping, index);
>> +		ASSERT(!IS_ERR(folio));
>> +		in_data = kmap_local_folio(folio,
>> +				offset_in_folio(folio, (u64)index << PAGE_SHIFT));
> 
> It would be better to avoid the cast, this is source of subtle errors so
> we try to avoid that. With demise of 32bit architectures it's less of a
> problem because index (pgoff_t) is 64 bit type but still.
> 
> Please insert a patch that changes the type of index and index_end to
> u64, we initialize them from a u64 type anyway and we know the value
> fits to pgoff_t (as argument to filemap_get_folio()).
> 

Makes sense, will do.