linux-ext4 - Re: [PATCH v2 8/8] ext4: enable large folio for regular file

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Message-ID: <20250626145647.GA217371@mit.edu>
Date: Thu, 26 Jun 2025 10:56:47 -0400
From: "Theodore Ts'o" <tytso@....edu>
To: Zhang Yi <yi.zhang@...weicloud.com>
Cc: "D, Suneeth" <Suneeth.D@....com>, linux-ext4@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        willy@...radead.org, adilger.kernel@...ger.ca, jack@...e.cz,
        yi.zhang@...wei.com, libaokun1@...wei.com, yukuai3@...wei.com,
        yangerkun@...wei.com
Subject: Re: [PATCH v2 8/8] ext4: enable large folio for regular file

On Thu, Jun 26, 2025 at 09:26:41PM +0800, Zhang Yi wrote:
> 
> Thanks for the report, I will try to reproduce this performance regression on
> my machine and find out what caused this regression.

I took a quick look at this, and I *think* it's because lmbench is
measuring the latency of mmap read's --- I'm going to guess 4k random
page faults, but I'm not sure.  If that's the case, this may just be a
natural result of using large folios, and the tradeoff of optimizing
for large reads versus small page faults.

But if you could take a closer look, that would be great, thanks!

						- Ted