Re: [PATCH rfc 1/9] mm: migrate: simplify __buffer_migrate_folio()

From: Matthew Wilcox <willy@infradead.org>
To: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, Tony Luck <tony.luck@intel.com>,
	Naoya Horiguchi <naoya.horiguchi@nec.com>,
	Miaohe Lin <linmiaohe@huawei.com>,
	David Hildenbrand <david@redhat.com>,
	Muchun Song <muchun.song@linux.dev>,
	Benjamin LaHaise <bcrl@kvack.org>,
	jglisse@redhat.com, linux-aio@kvack.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH rfc 1/9] mm: migrate: simplify __buffer_migrate_folio()
Date: Thu, 1 Feb 2024 19:12:25 +0000	[thread overview]
Message-ID: <ZbvtGWphK1uGg25J@casper.infradead.org> (raw)
In-Reply-To: <20240129070934.3717659-2-wangkefeng.wang@huawei.com>

On Mon, Jan 29, 2024 at 03:09:26PM +0800, Kefeng Wang wrote:
> @@ -774,24 +774,16 @@ static int __buffer_migrate_folio(struct address_space *mapping,
>  		}
>  	}
>  
> -	rc = folio_migrate_mapping(mapping, dst, src, 0);
> +	rc = filemap_migrate_folio(mapping, dst, src, mode);
>  	if (rc != MIGRATEPAGE_SUCCESS)
>  		goto unlock_buffers;
>  
> -	folio_attach_private(dst, folio_detach_private(src));
> -
>  	bh = head;
>  	do {
>  		folio_set_bh(bh, dst, bh_offset(bh));
>  		bh = bh->b_this_page;
>  	} while (bh != head);
>  
> -	if (mode != MIGRATE_SYNC_NO_COPY)
> -		folio_migrate_copy(dst, src);
> -	else
> -		folio_migrate_flags(dst, src);
> -
> -	rc = MIGRATEPAGE_SUCCESS;

I wondered if maybe there was an ordering requirement; that we had to
set up the BHs before copying the data over.  But I don't think there
is; the page should be frozen, the buffer heads are locked, and I don't
think the ordering matters.  So ...

Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>