Received-SPF: pass (google.com: domain of linux-kernel+bounces-199117-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Date: Mon, 3 Jun 2024 13:36:46 +0100
From: Matthew Wilcox <willy@infradead.org>
To: "Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>
Cc: david@fromorbit.com, chandan.babu@oracle.com, akpm@linux-foundation.org,
	brauner@kernel.org, djwong@kernel.org, linux-kernel@vger.kernel.org,
	hare@suse.de, john.g.garry@oracle.com, gost.dev@samsung.com,
	yang@os.amperecomputing.com, p.raghav@samsung.com,
	cl@os.amperecomputing.com, linux-xfs@vger.kernel.org, hch@lst.de,
	mcgrof@kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v6 05/11] mm: split a folio in minimum folio order chunks
Message-ID: <Zl243qf2WiPHIMWN@casper.infradead.org>
References: <20240529134509.120826-1-kernel@pankajraghav.com>
 <20240529134509.120826-6-kernel@pankajraghav.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240529134509.120826-6-kernel@pankajraghav.com>

On Wed, May 29, 2024 at 03:45:03PM +0200, Pankaj Raghav (Samsung) wrote:
> @@ -3572,14 +3600,19 @@ static int split_huge_pages_in_file(const char *file_path, pgoff_t off_start,
>  
>  	for (index = off_start; index < off_end; index += nr_pages) {
>  		struct folio *folio = filemap_get_folio(mapping, index);
> +		unsigned int min_order, target_order = new_order;
>  
>  		nr_pages = 1;
>  		if (IS_ERR(folio))
>  			continue;
>  
> -		if (!folio_test_large(folio))
> +		if (!folio->mapping || !folio_test_large(folio))
>  			goto next;

This check is useless.  folio->mapping is set to NULL on truncate,
but you haven't done anything to prevent truncate yet.  That happens
later when you lock the folio.

> +		min_order = mapping_min_folio_order(mapping);

You should hoist this out of the loop.

> +		if (new_order < min_order)
> +			target_order = min_order;
> +
>  		total++;
>  		nr_pages = folio_nr_pages(folio);
>  
> @@ -3589,7 +3622,18 @@ static int split_huge_pages_in_file(const char *file_path, pgoff_t off_start,
>  		if (!folio_trylock(folio))
>  			goto next;
>  
> -		if (!split_folio_to_order(folio, new_order))
> +		if (!folio_test_anon(folio)) {

Please explain how a folio _in a file_ can be anon?

> +			unsigned int min_order;
> +
> +			if (!folio->mapping)
> +				goto next;
> +
> +			min_order = mapping_min_folio_order(folio->mapping);
> +			if (new_order < target_order)
> +				target_order = min_order;

Why is this being repeated?

> +		}
> +
> +		if (!split_folio_to_order(folio, target_order))
>  			split++;
>  
>  		folio_unlock(folio);
> -- 
> 2.34.1
>