linux-kernel - Re: [PATCH 4/6] mm: don't remap unused subpages when splitting isolated thp

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Message-ID: <20df6650c834b3d2d6e5d7062876ee6a1e997dba.camel@surriel.com>
Date: Tue, 30 Jul 2024 14:07:39 -0400
From: Rik van Riel <riel@...riel.com>
To: Usama Arif <usamaarif642@...il.com>, akpm@...ux-foundation.org, 
	linux-mm@...ck.org
Cc: hannes@...xchg.org, shakeel.butt@...ux.dev, roman.gushchin@...ux.dev, 
 yuzhao@...gle.com, david@...hat.com, baohua@...nel.org,
 ryan.roberts@....com,  rppt@...nel.org, willy@...radead.org,
 cerasuolodomenico@...il.com, corbet@....net,  linux-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, kernel-team@...a.com,  Shuang Zhai
 <zhais@...gle.com>
Subject: Re: [PATCH 4/6] mm: don't remap unused subpages when splitting
 isolated thp

On Tue, 2024-07-30 at 13:46 +0100, Usama Arif wrote:
> 
> +	/*
> +	 * The pmd entry mapping the old thp was flushed and the pte
> mapping
> +	 * this subpage has been non present. Therefore, this
> subpage is
> +	 * inaccessible. We don't need to remap it if it contains
> only zeros.
> +	 */
> +	addr = kmap_local_page(page);
> +	dirty = memchr_inv(addr, 0, PAGE_SIZE);
> +	kunmap_local(addr);
> +
> +	if (dirty)
> +		return false;
> 

A minor nitpick here. The word dirty has a few different meanings
in memory management already.

Could it be clearer to use something like "contains_data" ?

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