From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 132F4C2D0E2 for ; Tue, 22 Sep 2020 15:22:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8E3C723A34 for ; Tue, 22 Sep 2020 15:22:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Nk8D8afD" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726672AbgIVPWo (ORCPT ); Tue, 22 Sep 2020 11:22:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46018 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726566AbgIVPWo (ORCPT ); Tue, 22 Sep 2020 11:22:44 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D3F7EC061755 for ; Tue, 22 Sep 2020 08:22:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=47IgGGQcOCGVOf/10+SQlAajxJWXxBSCU0PDicFXtkQ=; b=Nk8D8afDKDMQRFSjD6NLhYDDGP 8z35Z+0f0THPgALMziI37cQjTCJ83agSD5D7eoYqE9haljcEWI/kCVHLIGD4ENNnOql3VNeo9Arjc mw1jdyE4ASIwoSoxoziaHqgP8Nx7KGZicQxCi/GeG2OhZJVKDom9fxV8wxAOBt25bAsz3HCJFZu6j zsalt0MTZFbDvLaqoZ7IKuRpo3F+nCB9xaaVz7X5bqj9x9cKL0RP8f7RwJzqIPRp0kWYWPqIN2kfu XO/UYZM2SXNX2ck6pdhPFWJTZOmu/qs/2fFcWVsPa+/pf2Rf05RMkWPTUQR/ts/HL6MVT6zCxwiWr Wm+tHVoQ==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kKk7s-0003rS-Ur; Tue, 22 Sep 2020 15:22:40 +0000 Date: Tue, 22 Sep 2020 16:22:40 +0100 From: Matthew Wilcox To: Christoph Hellwig Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Uladzislau Rezki Subject: Re: [PATCH 2/2] vfree: Update documentation Message-ID: <20200922152240.GI32101@casper.infradead.org> References: <20200921224628.20704-1-willy@infradead.org> <20200921224628.20704-2-willy@infradead.org> <20200922143506.GA26664@lst.de> <20200922150603.GH32101@casper.infradead.org> <20200922150910.GA29302@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200922150910.GA29302@lst.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 22, 2020 at 05:09:10PM +0200, Christoph Hellwig wrote: > On Tue, Sep 22, 2020 at 04:06:03PM +0100, Matthew Wilcox wrote: > > I don't think it makes sense to list all vmalloc-style allocators here. > > It won't be updated by people who add new variations. How about this? > > > > * Free the virtually continuous memory area starting at @addr, as > > * obtained from one of the vmalloc() family of APIs. This will > > * usually also free the physical memory underlying the virtual > > * allocation, but that memory is reference counted, so it will not > > * be freed until the last user goes away. > > * > > * If @addr is NULL, no operation is performed. > > > > I'm trying to strike a balance between being accurate and not requiring > > device driver authors to learn all about struct page. I may be too > > close to the implementation to write good documentation for it. > > I think the above is sensible, but not enough. vmap really needs to > be treated special, as by default area->pages for vmap is NULL. So > for vfree to be useful on a vmap mapping, the callers needs to > manually set it up by poking into the internals. Actually, I think > we really want another API rather than vmap for that. Let me respin > my series to include that. I've been thinking about somethng like: void *vmap_mapping(struct address_space *mapping, pgoff_t start, unsigned long len); but it doesn't quite work for the shmem cases because they need to use shmem_read_mapping_page_gfp() instead of ->readpage. I'd also want it to work for DAX, but I don't have a user for that yet so it's hard to justify adding it. I have ideas for making shmem/tmpfs work more like other filesystems, so we don't need shmem_read_mapping_page_gfp() but there are only so many hours in the day.