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

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Message-ID: <20220920085437.ngyrzgxe2uoi7g4a@techsingularity.net>
Date:   Tue, 20 Sep 2022 09:55:02 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     "zhaoyang.huang" <zhaoyang.huang@...soc.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Zhaoyang Huang <huangzhaoyang@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, ke.wang@...soc.com
Subject: Re: [PATCHv2] mm: check high-order page when free it to pcp

On Tue, Sep 20, 2022 at 08:49:00AM +0800, zhaoyang.huang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> 
> 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@...soc.com>

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