From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id 5CC556B0387 for ; Thu, 9 Feb 2017 15:15:23 -0500 (EST) Received: by mail-pf0-f197.google.com with SMTP id 204so20166043pfx.1 for ; Thu, 09 Feb 2017 12:15:23 -0800 (PST) Received: from bombadil.infradead.org (bombadil.infradead.org. [65.50.211.133]) by mx.google.com with ESMTPS id 85si11010074pfq.219.2017.02.09.12.15.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 09 Feb 2017 12:15:22 -0800 (PST) Date: Thu, 9 Feb 2017 12:14:16 -0800 From: Matthew Wilcox Subject: Re: [PATCHv6 05/37] thp: try to free page's buffers before attempt split Message-ID: <20170209201416.GS2267@bombadil.infradead.org> References: <20170126115819.58875-1-kirill.shutemov@linux.intel.com> <20170126115819.58875-6-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170126115819.58875-6-kirill.shutemov@linux.intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" Cc: Theodore Ts'o , Andreas Dilger , Jan Kara , Andrew Morton , Alexander Viro , Hugh Dickins , Andrea Arcangeli , Dave Hansen , Vlastimil Babka , Ross Zwisler , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-block@vger.kernel.org On Thu, Jan 26, 2017 at 02:57:47PM +0300, Kirill A. Shutemov wrote: > @@ -2146,6 +2146,23 @@ int split_huge_page_to_list(struct page *page, struct list_head *list) > goto out; > } > > + /* Try to free buffers before attempt split */ > + if (!PageSwapBacked(head) && PagePrivate(page)) { > + /* > + * We cannot trigger writeback from here due possible > + * recursion if triggered from vmscan, only wait. > + * > + * Caller can trigger writeback it on its own, if safe. > + */ It took me a few reads to get this. May I suggest: /* * Cannot split a page with buffers. If the caller has * already started writeback, we can wait for it to finish, * but we cannot start writeback if we were called from vmscan */ > + if (!PageSwapBacked(head) && PagePrivate(page)) { Also, it looks weird to test PageSwapBacked of *head* and PagePrivate of *page*. I think it's correct, but it still looks weird. Reviewed-by: Matthew Wilcox -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org