linux-kernel - Re: [RFC 03/23] filemap: add folio with at least mapping_min_order in __filemap_get

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Date:   Fri, 15 Sep 2023 20:00:06 +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 03/23] filemap: add folio with at least mapping_min_order
 in __filemap_get_folio

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.