linux-kernel - Re: [linus:master] [readahead] ab4443fe3c: vm-scalability.throughput -21.4% regression

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Message-ID: <d7ab3fd4-6c7a-4ff9-a870-535af51256e5@intel.com>
Date: Sun, 10 Mar 2024 14:41:42 +0800
From: "Yin, Fengwei" <fengwei.yin@...el.com>
To: Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>
CC: Yujie Liu <yujie.liu@...el.com>, Oliver Sang <oliver.sang@...el.com>,
	<oe-lkp@...ts.linux.dev>, <lkp@...el.com>, <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, Guo Xuenan <guoxuenan@...wei.com>,
	<linux-fsdevel@...r.kernel.org>, <ying.huang@...el.com>,
	<feng.tang@...el.com>
Subject: Re: [linus:master] [readahead] ab4443fe3c: vm-scalability.throughput
 -21.4% regression

Hi Matthew,

On 3/8/2024 2:19 AM, Matthew Wilcox wrote:
>   		/* Align with smaller pages if needed */
>   		if (index & ((1UL << order) - 1))
>   			order = __ffs(index);
> +		/* Avoid wrap */
> +		if (index + (1UL << order) == 0)
> +			order--;
>   		/* Don't allocate pages past EOF */
> -		while (index + (1UL << order) - 1 > limit)
> +		while (index + (1UL << order) - 1 > last)
The lockup is related with this line. When index == (last + 1),
deadloop here.


Regards
Yin, Fengwei

>   			order--;