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

From: "Yin, Fengwei" <fengwei.yin@intel.com>
To: Matthew Wilcox <willy@infradead.org>, Jan Kara <jack@suse.cz>
Cc: Yujie Liu <yujie.liu@intel.com>,
	Oliver Sang <oliver.sang@intel.com>, <oe-lkp@lists.linux.dev>,
	<lkp@intel.com>, <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Guo Xuenan <guoxuenan@huawei.com>,
	<linux-fsdevel@vger.kernel.org>, <ying.huang@intel.com>,
	<feng.tang@intel.com>
Subject: Re: [linus:master] [readahead] ab4443fe3c: vm-scalability.throughput -21.4% regression
Date: Sun, 10 Mar 2024 14:41:42 +0800	[thread overview]
Message-ID: <d7ab3fd4-6c7a-4ff9-a870-535af51256e5@intel.com> (raw)
In-Reply-To: <ZeoFQnVYLLBLNL6J@casper.infradead.org>

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--;