linux-kernel - Re: [RFC 02/23] pagemap: use mapping_min_order in fgf_set

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Date:   Wed, 20 Sep 2023 09:46:35 +0200
From:   Pankaj Raghav <p.raghav@...sung.com>
To:     Matthew Wilcox <willy@...radead.org>,
        Pankaj Raghav <kernel@...kajraghav.com>
CC:     <linux-xfs@...r.kernel.org>, <linux-fsdevel@...r.kernel.org>,
        <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 02/23] pagemap: use mapping_min_order in fgf_set_order()

On 2023-09-15 20:55, Matthew Wilcox wrote:
> On Fri, Sep 15, 2023 at 08:38:27PM +0200, Pankaj Raghav wrote:
>> From: Pankaj Raghav <p.raghav@...sung.com>
>>
>> fgf_set_order() encodes optimal order in fgp flags. Set it to at least
>> mapping_min_order from the page cache. Default to the old behaviour if
>> min_order is not set.
> 
> Why not simply:
> 

That is a good idea to move this to filemap instead of changing it in iomap. I will do that!

> +++ b/mm/filemap.c
> @@ -1906,9 +1906,12 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
>                 folio_wait_stable(folio);
>  no_page:
>         if (!folio && (fgp_flags & FGP_CREAT)) {
> -               unsigned order = FGF_GET_ORDER(fgp_flags);
> +               unsigned order;
>                 int err;
> 
> +               order = min(mapping_min_folio_order(mapping),
> +                               FGF_GET_ORDER(fgp_flags));
> 

I think this needs to max(mapping..., FGF...)