> On Feb 20, 2023, at 5:24 AM, Muhammad Usama Anjum <usama.anjum@xxxxxxxxxxxxx> wrote:
>
>>> +static inline int pagemap_scan_pmd_entry(pmd_t *pmd, unsigned long start,
>>> + unsigned long end, struct mm_walk *walk)
>>> +{
>>> + struct pagemap_scan_private *p = walk->private;
>>> + struct vm_area_struct *vma = walk->vma;
>>> + unsigned long addr = end;
>>> + spinlock_t *ptl;
>>> + int ret = 0;
>>> + pte_t *pte;
>>> +
>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>> + ptl = pmd_trans_huge_lock(pmd, vma);
>>> + if (ptl) {
>>> + bool pmd_wt;
>>> +
>>> + pmd_wt = !is_pmd_uffd_wp(*pmd);
>>> + /*
>>> + * Break huge page into small pages if operation needs to be
>>> performed is
>>> + * on a portion of the huge page.
>>> + */
>>> + if (pmd_wt && IS_WP_ENGAGE_OP(p) && (end - start < HPAGE_SIZE)) {
>>> + spin_unlock(ptl);
>>> + split_huge_pmd(vma, pmd, start);
>>> + goto process_smaller_pages;
>> I think that such goto's are really confusing and should be avoided. And
>> using 'else' (could have easily prevented the need for goto). It is not the
>> best solution though, since I think it would have been better to invert the
>> conditions.
> Yeah, else can be used here. But then we'll have to add a tab to all the
> code after adding else. We have already so many tabs and very less space to
> right code. Not sure which is better.
goto’s are usually not the right solution. You can extract things into a different
function if you have to.
I’m not sure why IS_GET_OP(p) might be false and what’s the meaning of taking the
lock and dropping it in such a case. I think that the code can be simplified and
additional condition nesting can be avoided.
>>> --- a/include/uapi/linux/fs.h
>>> +++ b/include/uapi/linux/fs.h
>>> @@ -305,4 +305,54 @@ typedef int __bitwise __kernel_rwf_t;
>>> #define RWF_SUPPORTED (RWF_HIPRI | RWF_DSYNC | RWF_SYNC | RWF_NOWAIT |\
>>> RWF_APPEND)
>>> +/* Pagemap ioctl */
>>> +#define PAGEMAP_SCAN _IOWR('f', 16, struct pagemap_scan_arg)
>>> +
>>> +/* Bits are set in the bitmap of the page_region and masks in
>>> pagemap_scan_args */
>>> +#define PAGE_IS_WRITTEN (1 << 0)
>>> +#define PAGE_IS_FILE (1 << 1)
>>> +#define PAGE_IS_PRESENT (1 << 2)
>>> +#define PAGE_IS_SWAPPED (1 << 3)
>>
>> These names are way too generic and are likely to be misused for the wrong
>> purpose. The "_IS_" part seems confusing as well. So I think the naming
>> needs to be fixed and some new type (using typedef) or enum should be
>> introduced to hold these flags. I understand it is part of uapi and it is
>> less common there, but it is not unheard of and does make things clearer.
> Do you think PM_SCAN_PAGE_IS_* work here?
Can we lose the IS somehow?
>
>>
>>
>>> +
>>> +/*
>>> + * struct page_region - Page region with bitmap flags
>>> + * @start: Start of the region
>>> + * @len: Length of the region
>>> + * bitmap: Bits sets for the region
>>> + */
>>> +struct page_region {
>>> + __u64 start;
>>> + __u64 len;
>>
>> I presume in bytes. Would be useful to mention.
> Length of region in pages.
Very unintuitive to me I must say. If the start is an address, I would expect
the len to be in bytes.
