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

On 6/22/26 08:45, Chao Yu via Linux-f2fs-devel wrote:
> On 6/22/26 00:07, Yongpeng Yang wrote:
>>
>> On 6/20/26 2:15 PM, Chao Yu via Linux-f2fs-devel wrote:
>>> 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?
>>
>> The only distinction between punch and drop arises when the largest
>> extent is not present in the extent tree.
>>
>> Before this patch(extent format [fofs, len, blk])
>> 1. inital state
>>      largest extent: [0, 1024, 10], extent tree: empty
> 
>                                                    ^^^^^
> 
> It's not empty w/o patch 2/5.

Sorry for the confusion. "empty" means that the largest extent has been
shrunk.

Thanks
Yongpeng,

> 
> Thanks,
> 
>> 2. insert [511, 1, 10000]
>>      largest extent: [511, 1, 10000], extent tree: [511, 1, 10000]
>>
>> After this patch:
>> 1. inital state
>>      largest extent: [0, 1024, 10], extent tree: empty
>> 2. insert [511, 1, 10000]
>>      largest extent: [512, 512, 522], extent tree: [511, 1, 10000]
>>
>> Thanks
>> Yongpeng,
>>
>>>
>>> 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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>>
> 
> 
> 
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