Re: [PATCH v3 1/2] mm: pass page count and reserved to __init_single_page

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On 2023/9/26 15:44, David Hildenbrand wrote:
On 26.09.23 04:33, Yajun Deng wrote:
When we init a single page, we need to mark this page reserved if it
does.

I failed to parse the last part of this sentence.

And some pages may not need to set page count, such as compound
pages.

Usually, the refcount of all tail pages *must* be zero. Otherwise, get_page_unless_zero() would work on tail pages.

Can you elaborate why it should be okay here?


It means the following code in memmap_init_compound().

-               __init_zone_device_page(page, pfn, zone_idx, nid, pgmap);
+               __init_zone_device_page(page, pfn, zone_idx, nid, pgmap, 0);
                prep_compound_tail(head, pfn - head_pfn);
                set_page_count(page, 0);

As we can see, it will reset the page count by 'set_page_count(page, 0)'.

Therefore, we don't need to set page count in __init_zone_device_page(). I wasn't clear enough in the commit.

Maybe we can remove the 'set_page_count(page, 0)',  But I didn't do that, just to be safe.





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