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

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.

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 &&
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> Linux-f2fs-devel mailing list
>>>> [email protected]
>>>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>>>
>>
>>
>>
>> _______________________________________________
>> Linux-f2fs-devel mailing list
>> [email protected]
>> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
> 



_______________________________________________
Linux-f2fs-devel mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel