[PATCH 2/3] mm: Add folio_fill_tail() and use it in iomap

[Gao Xiang]

On 2023/11/11 01:09, Matthew Wilcox wrote:
> On Thu, Nov 09, 2023 at 10:50:45PM +0100, Andreas Gruenbacher wrote:
>> On Tue, Nov 7, 2023 at 10:27 PM Matthew Wilcox (Oracle)
>> <willy at infradead.org> wrote:
>>> +static inline void folio_fill_tail(struct folio *folio, size_t offset,
>>> +               const char *from, size_t len)
>>> +{
>>> +       char *to = kmap_local_folio(folio, offset);
>>> +
>>> +       VM_BUG_ON(offset + len > folio_size(folio));
>>> +
>>> +       if (folio_test_highmem(folio)) {
>>> +               size_t max = PAGE_SIZE - offset_in_page(offset);
>>> +
>>> +               while (len > max) {
>>> +                       memcpy(to, from, max);
>>> +                       kunmap_local(to);
>>> +                       len -= max;
>>> +                       from += max;
>>> +                       offset += max;
>>> +                       max = PAGE_SIZE;
>>> +                       to = kmap_local_folio(folio, offset);
>>> +               }
>>> +       }
>>> +
>>> +       memcpy(to, from, len);
>>> +       to = folio_zero_tail(folio, offset, to);
>>
>> This needs to be:
>>
>> to = folio_zero_tail(folio, offset  + len, to + len);
> 
> Oh, wow, that was stupid of me.  I only ran an xfstests against ext4,
> which doesn't exercise this code, not gfs2 or erofs.  Thanks for
> fixing this up.

Assuming that is for the next cycle (no rush), I will also test
this patch and feedback later since I'm now working on other
stuffs.

Thanks,
Gao Xiang