From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 54B44131E40 for ; Tue, 6 Feb 2024 14:53:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707231182; cv=none; b=O5GfA4on6XmmY0dcR+Aj7+6lMgIRmZZKcQz5xmTJ/PIJRs+YXb+WUTeRP1gfwJWIJSKhfXUY6hheYnbGMs88spx4UWsjfSPv9VTWxdWVbhGR/AVInihKMtgefe+WNLEcKZY5bH8L2bYl5Awu4WWdC/z4XBlsoCDjPcQGqNw3g6M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707231182; c=relaxed/simple; bh=Qrpa+uGtUHpG2JAA82HSPm/TG8ygOkhkTJPlA2/C7bk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QHsxCJmgsaYC14VL1/sL/J784xoeSaGyYkSZ6u8GKSo3oW12el3uV6Q4FTpQPUyO5JNUa8JvhpZpsrH0mOFkiUWjoHThnlDSbTGuWFPi69BYTkoaIKHSnFaWE7DdH6SL9B3k/DsGXtkGLRfBmEtd8xHXXLGtxVzQ5cUhfj6/7tc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=gUFwmlLy; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="gUFwmlLy" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1707231179; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=ICNu3j0RxsXSNnJAkw6sqT5jyTGFKxvpyFp2l0saKd0=; b=gUFwmlLyUTv+FSy7TwyByfEk65+c6VtBgMLiZc0vcEgK+N1Iq5cyQ9etA0QfDezcyq+GNd dupOelTyCT6IXw3oBiDHk5vwF6VLYhecA/BXQfXGJssZZLokqpagaikg5bVNqcu3oa6Epu RehTYZN7EONhLsEncHlundNFdplooLo= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-167-zB82_cyAMDOOlBX9rRInSA-1; Tue, 06 Feb 2024 09:52:44 -0500 X-MC-Unique: zB82_cyAMDOOlBX9rRInSA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id D5715185A782; Tue, 6 Feb 2024 14:52:43 +0000 (UTC) Received: from bfoster (unknown [10.22.32.186]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6A5E51C060B3; Tue, 6 Feb 2024 14:52:43 +0000 (UTC) Date: Tue, 6 Feb 2024 09:54:01 -0500 From: Brian Foster To: Christoph Hellwig Cc: linux-mm@kvack.org, Matthew Wilcox , Jan Kara , David Howells , Christian Brauner , "Darrick J. Wong" , linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 12/13] writeback: add a writeback iterator Message-ID: References: <20240203071147.862076-1-hch@lst.de> <20240203071147.862076-13-hch@lst.de> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7 On Mon, Feb 05, 2024 at 10:33:52AM -0500, Brian Foster wrote: > On Sat, Feb 03, 2024 at 08:11:46AM +0100, Christoph Hellwig wrote: > > Refactor the code left in write_cache_pages into an iterator that the > > file system can call to get the next folio for a writeback operation: > > > > struct folio *folio = NULL; > > > > while ((folio = writeback_iter(mapping, wbc, folio, &error))) { > > error = ; > > } > > > > The twist here is that the error value is passed by reference, so that > > the iterator can restore it when breaking out of the loop. > > > > Handling of the magic AOP_WRITEPAGE_ACTIVATE value stays outside the > > iterator and needs is just kept in the write_cache_pages legacy wrapper. > > in preparation for eventually killing it off. > > > > Heavily based on a for_each* based iterator from Matthew Wilcox. > > > > Signed-off-by: Christoph Hellwig > > --- > > include/linux/writeback.h | 4 + > > mm/page-writeback.c | 192 ++++++++++++++++++++++---------------- > > 2 files changed, 118 insertions(+), 78 deletions(-) > > > ... > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > > index 3abb053e70580e..5fe4cdb7dbd61a 100644 > > --- a/mm/page-writeback.c > > +++ b/mm/page-writeback.c > ... > > @@ -2434,69 +2434,68 @@ static struct folio *writeback_get_folio(struct address_space *mapping, > > } > > > > /** > ... > > */ > > -int write_cache_pages(struct address_space *mapping, > > - struct writeback_control *wbc, writepage_t writepage, > > - void *data) > > +struct folio *writeback_iter(struct address_space *mapping, > > + struct writeback_control *wbc, struct folio *folio, int *error) > > { > ... > > + } else { > > wbc->nr_to_write -= folio_nr_pages(folio); > > > > - if (error == AOP_WRITEPAGE_ACTIVATE) { > > - folio_unlock(folio); > > - error = 0; > > - } > > + WARN_ON_ONCE(*error > 0); > > Why the warning on writeback error here? It looks like new behavior, but > maybe I missed something. Otherwise the factoring LGTM. Err, sorry.. I glossed over the > 0 check and read it as < 0. Disregard, this seems reasonable to me as long as we no longer expect those AOP returns (which I'm not really clear on either, but anyways..): Reviewed-by: Brian Foster > > Brian > > > > > /* > > * For integrity writeback we have to keep going until we have > > @@ -2510,33 +2509,70 @@ int write_cache_pages(struct address_space *mapping, > > * wbc->nr_to_write or encounter the first error. > > */ > > if (wbc->sync_mode == WB_SYNC_ALL) { > > - if (error && !ret) > > - ret = error; > > + if (*error && !wbc->saved_err) > > + wbc->saved_err = *error; > > } else { > > - if (error || wbc->nr_to_write <= 0) > > + if (*error || wbc->nr_to_write <= 0) > > goto done; > > } > > } > > > > - /* > > - * For range cyclic writeback we need to remember where we stopped so > > - * that we can continue there next time we are called. If we hit the > > - * last page and there is more work to be done, wrap back to the start > > - * of the file. > > - * > > - * For non-cyclic writeback we always start looking up at the beginning > > - * of the file if we are called again, which can only happen due to > > - * -ENOMEM from the file system. > > - */ > > - folio_batch_release(&wbc->fbatch); > > - if (wbc->range_cyclic) > > - mapping->writeback_index = 0; > > - return ret; > > + folio = writeback_get_folio(mapping, wbc); > > + if (!folio) { > > + /* > > + * To avoid deadlocks between range_cyclic writeback and callers > > + * that hold pages in PageWriteback to aggregate I/O until > > + * the writeback iteration finishes, we do not loop back to the > > + * start of the file. Doing so causes a page lock/page > > + * writeback access order inversion - we should only ever lock > > + * multiple pages in ascending page->index order, and looping > > + * back to the start of the file violates that rule and causes > > + * deadlocks. > > + */ > > + if (wbc->range_cyclic) > > + mapping->writeback_index = 0; > > + > > + /* > > + * Return the first error we encountered (if there was any) to > > + * the caller. > > + */ > > + *error = wbc->saved_err; > > + } > > + return folio; > > > > done: > > folio_batch_release(&wbc->fbatch); > > if (wbc->range_cyclic) > > mapping->writeback_index = folio->index + folio_nr_pages(folio); > > + return NULL; > > +} > > + > > +/** > > + * write_cache_pages - walk the list of dirty pages of the given address space and write all of them. > > + * @mapping: address space structure to write > > + * @wbc: subtract the number of written pages from *@wbc->nr_to_write > > + * @writepage: function called for each page > > + * @data: data passed to writepage function > > + * > > + * Return: %0 on success, negative error code otherwise > > + * > > + * Note: please use writeback_iter() instead. > > + */ > > +int write_cache_pages(struct address_space *mapping, > > + struct writeback_control *wbc, writepage_t writepage, > > + void *data) > > +{ > > + struct folio *folio = NULL; > > + int error; > > + > > + while ((folio = writeback_iter(mapping, wbc, folio, &error))) { > > + error = writepage(folio, wbc, data); > > + if (error == AOP_WRITEPAGE_ACTIVATE) { > > + folio_unlock(folio); > > + error = 0; > > + } > > + } > > + > > return error; > > } > > EXPORT_SYMBOL(write_cache_pages); > > -- > > 2.39.2 > > > > > >