linux-kernel - Re: [RFC 01/23] fs: Allow fine-grained control of folio sizes

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Date:   Fri, 15 Sep 2023 20:03:14 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Pankaj Raghav <kernel@...kajraghav.com>
Cc:     linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        p.raghav@...sung.com, david@...morbit.com, da.gomez@...sung.com,
        akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        djwong@...nel.org, linux-mm@...ck.org, chandan.babu@...cle.com,
        mcgrof@...nel.org, gost.dev@...sung.com
Subject: Re: [RFC 01/23] fs: Allow fine-grained control of folio sizes

On Fri, Sep 15, 2023 at 08:38:26PM +0200, Pankaj Raghav wrote:
> +static inline void mapping_set_folio_orders(struct address_space *mapping,
> +					    unsigned int min, unsigned int max)
> +{
> +	/*
> +	 * XXX: max is ignored as only minimum folio order is supported
> +	 * currently.
> +	 */

I think we need some sanity checking ...

	if (min == 1)
		min = 2;
	if (max < min)
		max = min;
	if (max > MAX_PAGECACHE_ORDER)
		max = MAX_PAGECACHE_ORDER;

> +	mapping->flags = (mapping->flags & ~AS_FOLIO_ORDER_MASK) |
> +			 (min << AS_FOLIO_ORDER_MIN) |
> +			 (MAX_PAGECACHE_ORDER << AS_FOLIO_ORDER_MAX);
> +}