Re: [f2fs-dev] [PATCH RESEND 3/5] f2fs: punch largest extent instead of dropping it entirely on overlap

On 6/19/26 22:38, Yongpeng Yang wrote:
> 
> On 6/15/26 8:05 PM, Chao Yu via Linux-f2fs-devel wrote:
>> On 6/12/26 19:58, Yongpeng Yang wrote:
>>> From: Yongpeng Yang <[email protected]>
>>>
>>> Previously, when an extent being inserted overlaps with the largest
>>> extent, the largest extent is dropped entirely. This was done to handle
>>
>> Please correct me if I missed anything, I remember that we will add largest
>> extent in below path?
>>
>> - __update_extent_tree_range
>>   - __insert_extent_tree
>>    - __try_update_largest_extent : update largest w/ right extent
>>   - __try_update_largest_extent : update largest w/ left extent
> 
> The largest extent might not reside in the extent tree. If
> __update_extent_tree_range invokes __drop_largest_extent, the length of

I meant __update_extent_tree_range invokes __drop_largest_extent to drop
largest first, and then, it tries to update largest extent w/ larger-size
one of separated two extents.

> the largest extent will have been set to zero. As a result, the largest
> extent updated inside __try_update_largest_extent can end up smaller
> than the largest extent obtained after __punch_largest_extent completes
> its punch operation.

I didn't get it, can you give an example for this?

Thanks,

> 
> Thanks
> Yongpeng,
> 
>>
>> Thanks,
>>
>>> the case where the largest extent is not in memory, avoiding
>>> inconsistency between the largest extent and the extent tree.
>>>
>>> This patch changes the semantics of __drop_largest_extent (renamed to
>>> __punch_largest_extent): instead of discarding the entire largest
>>> extent when any overlap is detected, keep the larger remaining portion
>>> (left or right) after the punch. This preserves extent cache coverage
>>> for truncate and overwrite operations that only partially overlap the
>>> largest extent.
>>>
>>> Signed-off-by: Yongpeng Yang <[email protected]>
>>> ---
>>>   fs/f2fs/extent_cache.c | 31 ++++++++++++++++++++++++-------
>>>   1 file changed, 24 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c
>>> index f8d94db60dc6..82d84c4e98b2 100644
>>> --- a/fs/f2fs/extent_cache.c
>>> +++ b/fs/f2fs/extent_cache.c
>>> @@ -397,14 +397,31 @@ static unsigned int __free_extent_tree(struct f2fs_sb_info *sbi,
>>>       return count;
>>>   }
>>> -static void __drop_largest_extent(struct extent_tree *et,
>>> +static void __punch_largest_extent(struct extent_tree *et,
>>>                       pgoff_t fofs, unsigned int len)
>>>   {
>>> -    if (fofs < (pgoff_t)et->largest.fofs + et->largest.len &&
>>> -            fofs + len > et->largest.fofs) {
>>> -        et->largest.len = 0;
>>> -        et->largest_updated = true;
>>> +    unsigned int largest_end, punch_end;
>>> +    unsigned int left_len, right_len;
>>> +
>>> +    if (fofs >= (pgoff_t)et->largest.fofs + et->largest.len ||
>>> +            fofs + len <= et->largest.fofs)
>>> +        return;
>>> +
>>> +    /* Punch [fofs, fofs + len) from largest extent. */
>>> +    largest_end = et->largest.fofs + et->largest.len;
>>> +    punch_end = fofs + len;
>>> +
>>> +    left_len = fofs > et->largest.fofs ? fofs - et->largest.fofs : 0;
>>> +    right_len = largest_end > punch_end ? largest_end - punch_end : 0;
>>> +
>>> +    if (left_len >= right_len) {
>>> +        et->largest.len = left_len;
>>> +    } else {
>>> +        et->largest.blk += punch_end - et->largest.fofs;
>>> +        et->largest.fofs = punch_end;
>>> +        et->largest.len = right_len;
>>>       }
>>> +    et->largest_updated = true;
>>>   }
>>>   void f2fs_init_read_extent_tree(struct inode *inode, struct folio *ifolio)
>>> @@ -680,10 +697,10 @@ static void __update_extent_tree_range(struct inode *inode,
>>>           dei.len = 0;
>>>           /*
>>> -         * drop largest extent before lookup, in case it's already
>>> +         * punch largest extent before lookup, in case it's already
>>>            * been shrunk from extent tree
>>>            */
>>> -        __drop_largest_extent(et, fofs, len);
>>> +        __punch_largest_extent(et, fofs, len);
>>>       }
>>>       if (et->largest.len != 0 &&
>>
>>
>>
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> 



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