linux-kernel - Re:Re: [PATCH v1] mm/contpte: Optimize loop to reduce redundant operations

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <5e3f976f.bca1.19610528896.Coremail.xavier_qy@163.com>
Date: Mon, 7 Apr 2025 20:56:06 +0800 (CST)
From: Xavier  <xavier_qy@....com>
To: "Lance Yang" <ioworker0@...il.com>
Cc: akpm@...ux-foundation.org, baohua@...nel.org, catalin.marinas@....com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	ryan.roberts@....com, will@...nel.org
Subject: Re:Re: [PATCH v1] mm/contpte: Optimize loop to reduce redundant
 operations



Hi Lance,

Thanks for your feedback, my response is as follows.

--
Thanks,
Xavier





At 2025-04-07 19:29:22, "Lance Yang" <ioworker0@...il.com> wrote:
>Thanks for the patch. Would the following change be better?
>
>diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c
>index 55107d27d3f8..64eb3b2fbf06 100644
>--- a/arch/arm64/mm/contpte.c
>+++ b/arch/arm64/mm/contpte.c
>@@ -174,6 +174,9 @@ pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte)
> 
> 		if (pte_young(pte))
> 			orig_pte = pte_mkyoung(orig_pte);
>+
>+		if (pte_young(orig_pte) && pte_dirty(orig_pte))
>+			break;
> 	}
> 
> 	return orig_pte;
>-- 
>
>We can check the orig_pte flags directly instead of using extra boolean
>variables, which gives us an early-exit when both dirty and young flags
>are set.
Your way of writing the code is indeed more concise. However, I think
 using boolean variables might be more efficient. Although it introduces
 additional variables, comparing boolean values is likely to be more
 efficient than checking bit settings.

>
>Also, is this optimization really needed for the common case?
This function is on a high-frequency execution path. During debugging,
 I found that in most cases, the first few pages are already marked as
 both dirty and young. But currently, the program still has to complete
 the entire loop of 16 ptep iterations, which seriously reduces the efficiency.
>
>Thanks,
>Lance