linux-kernel - Re: [PATCH v5 09/12] khugepaged: avoid unnecessary mTHP collapse attempts

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Message-ID: <ba59d6aa-ade3-4440-a0ed-ef276b45f9d2@linux.alibaba.com>
Date: Wed, 30 Apr 2025 18:12:33 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Nico Pache <npache@...hat.com>, linux-mm@...ck.org,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org
Cc: akpm@...ux-foundation.org, corbet@....net, rostedt@...dmis.org,
 mhiramat@...nel.org, mathieu.desnoyers@...icios.com, david@...hat.com,
 baohua@...nel.org, ryan.roberts@....com, willy@...radead.org,
 peterx@...hat.com, ziy@...dia.com, wangkefeng.wang@...wei.com,
 usamaarif642@...il.com, sunnanyong@...wei.com, vishal.moola@...il.com,
 thomas.hellstrom@...ux.intel.com, yang@...amperecomputing.com,
 kirill.shutemov@...ux.intel.com, aarcange@...hat.com, raquini@...hat.com,
 dev.jain@....com, anshuman.khandual@....com, catalin.marinas@....com,
 tiwai@...e.de, will@...nel.org, dave.hansen@...ux.intel.com, jack@...e.cz,
 cl@...two.org, jglisse@...gle.com, surenb@...gle.com, zokeefe@...gle.com,
 hannes@...xchg.org, rientjes@...gle.com, mhocko@...e.com,
 rdunlap@...radead.org, lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com
Subject: Re: [PATCH v5 09/12] khugepaged: avoid unnecessary mTHP collapse
 attempts



On 2025/4/29 02:12, Nico Pache wrote:
> There are cases where, if an attempted collapse fails, all subsequent
> orders are guaranteed to also fail. Avoid these collapse attempts by
> bailing out early.
> 
> Signed-off-by: Nico Pache <npache@...hat.com>
> ---
>   mm/khugepaged.c | 17 +++++++++++++++++
>   1 file changed, 17 insertions(+)
> 
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 86d1153ce9e8..5e6732cccb86 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1365,6 +1365,23 @@ static int khugepaged_scan_bitmap(struct mm_struct *mm, unsigned long address,
>   				collapsed += (1 << order);
>   				continue;
>   			}
> +			/*
> +			 * Some ret values indicate all lower order will also
> +			 * fail, dont trying to collapse smaller orders
> +			 */
> +			if (ret == SCAN_EXCEED_NONE_PTE ||
> +				ret == SCAN_EXCEED_SWAP_PTE ||
> +				ret == SCAN_EXCEED_SHARED_PTE ||
> +				ret == SCAN_PTE_NON_PRESENT ||
> +				ret == SCAN_PTE_UFFD_WP ||
> +				ret == SCAN_ALLOC_HUGE_PAGE_FAIL ||
> +				ret == SCAN_CGROUP_CHARGE_FAIL ||
> +				ret == SCAN_COPY_MC ||
> +				ret == SCAN_PAGE_LOCK ||
> +				ret == SCAN_PAGE_COUNT)
> +				goto next;
> +			else
> +				break;

Better to merge this patch into patch 6, which can be helped to 
understand your logic.