Re: [PATCHv2] mm: check high-order page when free it to pcp

[Mel Gorman]

On Tue, Sep 20, 2022 at 08:49:00AM +0800, zhaoyang.huang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> 
> High-order pcp page escaped from checking when both of DEBUG_VM and debug_pagealloc
> are all disabled if it allocated again from pcp_list without going to global
> free list, which should be introduced by 44042b4498.
> 
> fix:44042b4498
> 
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>

Why is the order check needed? In this case, I think the comment itself was
wrong and should be corrected. free_pcp_prepare is called when dealing with
a PCP page being freed and these days that may order-0 or high-order pages.
Wieh DEBUG_VM disabled, the pages are checked in by bulkfree_pcp_prepare
when freeing pages from PCP to the core allocator. Why would just
high-order pages be checked in free_pcp_prepare and checked again in
bulkfree_pcp_prepare?

-- 
Mel Gorman
SUSE Labs