Received-SPF: pass (google.com: domain of linux-kernel+bounces-199095-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Date: Mon, 3 Jun 2024 13:18:45 +0100
From: Matthew Wilcox <willy@infradead.org>
To: "Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>
Cc: david@fromorbit.com, chandan.babu@oracle.com, akpm@linux-foundation.org,
	brauner@kernel.org, djwong@kernel.org, linux-kernel@vger.kernel.org,
	hare@suse.de, john.g.garry@oracle.com, gost.dev@samsung.com,
	yang@os.amperecomputing.com, p.raghav@samsung.com,
	cl@os.amperecomputing.com, linux-xfs@vger.kernel.org, hch@lst.de,
	mcgrof@kernel.org, linux-mm@kvack.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v6 03/11] filemap: allocate mapping_min_order folios in
 the page cache
Message-ID: <Zl20pc-YlIWCSy6Z@casper.infradead.org>
References: <20240529134509.120826-1-kernel@pankajraghav.com>
 <20240529134509.120826-4-kernel@pankajraghav.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240529134509.120826-4-kernel@pankajraghav.com>

On Wed, May 29, 2024 at 03:45:01PM +0200, Pankaj Raghav (Samsung) wrote:
> @@ -1919,8 +1921,10 @@ 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 int min_order = mapping_min_folio_order(mapping);
> +		unsigned int order = max(min_order, FGF_GET_ORDER(fgp_flags));
>  		int err;
> +		index = mapping_align_start_index(mapping, index);
>  
>  		if ((fgp_flags & FGP_WRITE) && mapping_can_writeback(mapping))
>  			gfp |= __GFP_WRITE;
> @@ -1958,7 +1962,7 @@ struct folio *__filemap_get_folio(struct address_space *mapping, pgoff_t index,
>  				break;
>  			folio_put(folio);
>  			folio = NULL;
> -		} while (order-- > 0);
> +		} while (order-- > min_order);

I'd argue you also need to change:

-                       if (order > 0)
+			if (order > min_order)
                                alloc_gfp |= __GFP_NORETRY | __GFP_NOWARN;

since that is the last point at which we can fall back.  If we can't
immediately allocate a min_order folio, we want to retry, and we
want to warn if we can't get it.