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

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Date:   Fri, 15 Sep 2023 19:55:12 +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 02/23] pagemap: use mapping_min_order in fgf_set_order()

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:

+++ 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));