On 31 Mar 2021, at 12:44, Matthew Wilcox wrote:
> On Mon, Mar 29, 2021 at 11:39:32AM -0400, Zi Yan wrote:
>> + for (off_cur = off_start; off_cur < off_end;) {
>> + struct page *fpage = pagecache_get_page(mapping, off_cur,
>> + FGP_ENTRY | FGP_HEAD, 0);
>> +
>> + if (xa_is_value(fpage) || !fpage) {
>> + off_cur += PAGE_SIZE;
>> + continue;
>> + }
>> +
>> + if (!is_transparent_hugepage(fpage)) {
>> + off_cur += PAGE_SIZE;
>> + goto next;
>> + }
>> + total++;
>> + off_cur = fpage->index + thp_size(fpage);
>
> That can't be right. fpage->index is in units of pages and thp_size is
> in units of bytes. I wish C had a better type system.
> I think you meant:
>
> off_cur = fpage->index + thp_nr_pages(fpage);
>
> Also, I think this loop would read better as ...
>
> for (index = off_start; index < off_end; index += nr_pages) {
> struct page *fpage = pagecache_get_page(mapping, index,
> FGP_ENTRY | FGP_HEAD, 0);
> nr_pages = 1;
> if (xa_is_value(fpage) || !fpage)
> continue;
> if (!is_transparent_hugepage(fpage))
> goto next;
> total++;
> nr_pages = thp_nr_pages(fpage);
> ...
Thanks for catching this! I mixed this with looping through VMA, which
is in units of bytes. I will fix this and use your suggested loop code.
—
Best Regards,
Yan Zi
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