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Date:   Fri, 15 Sep 2023 20:00:06 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Pankaj Raghav <kernel@pankajraghav.com>
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Subject: Re: [RFC 03/23] filemap: add folio with at least mapping_min_order
 in __filemap_get_folio
Message-ID: <ZQSpthmXGzHDbx1h@casper.infradead.org>
References: <20230915183848.1018717-1-kernel@pankajraghav.com>
 <20230915183848.1018717-4-kernel@pankajraghav.com>
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On Fri, Sep 15, 2023 at 08:38:28PM +0200, Pankaj Raghav wrote:
> +++ b/mm/filemap.c
> @@ -1862,6 +1862,10 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
>  		fgf_t fgp_flags, gfp_t gfp)
>  {
>  	struct folio *folio;
> +	int min_order = mapping_min_folio_order(mapping);
> +	int nr_of_pages = (1U << min_order);
> +
> +	index = round_down(index, nr_of_pages);
>  
>  repeat:
>  	folio = filemap_get_entry(mapping, index);
> @@ -1929,8 +1933,14 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
>  			err = -ENOMEM;
>  			if (order == 1)
>  				order = 0;
> +			if (order < min_order)
> +				order = min_order;

... oh, you do something similar here to what I recommend in my previous
response.  I don't understand why you need the previous patch.

> +			if (min_order)
> +				VM_BUG_ON(index & ((1UL << order) - 1));

You don't need the 'if' here; index & ((1 << 0) - 1) becomes false.