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=-8.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 E361DC12002 for ; Wed, 21 Jul 2021 14:12:20 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7947961246 for ; Wed, 21 Jul 2021 14:12:20 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7947961246 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 16AC96B0081; Wed, 21 Jul 2021 10:12:20 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 11B726B0082; Wed, 21 Jul 2021 10:12:20 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 030056B0083; Wed, 21 Jul 2021 10:12:19 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0003.hostedemail.com [216.40.44.3]) by kanga.kvack.org (Postfix) with ESMTP id DBB3F6B0081 for ; Wed, 21 Jul 2021 10:12:19 -0400 (EDT) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 957CB18575939 for ; Wed, 21 Jul 2021 14:12:19 +0000 (UTC) X-FDA: 78386784798.23.2D0EC90 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf28.hostedemail.com (Postfix) with ESMTP id EF7B9900C53B for ; Wed, 21 Jul 2021 14:12:18 +0000 (UTC) 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=pCqdwefLOL0fhBrx/OBvnT5ccjRgtPGA+iSizhy+8vw=; b=ZIkbTOlnfMdhdbTbZj82Cs/2GN c5CiRzbRJ62q+oZagyh6yMQsS0MfMC7fxPfxd6IWOwCHSMGJyvAHCJg1VQeC/KAwdi1W82gK/37Dd xrFgudNbSVrauIKc13XQKvvT5ljxlNmLhwMR7edOzu91h19OBXIxTNG0byYiBoTO0OUCod2UPBOCA Beib9ruIADNIxQaMzE7EdUh9KjlUDd1EcRxX2DY8Xjfsc+37X4VbwnkscG9Vj85IUInEWjDX9tIyL ks9DgKgTtwXLEJ5p5rwSQ1nDcPvdaL4vyfm52ZZVspUUgZD294+/InP9LR5wHpim5/P2pvu1DVCN8 18hMeDCg==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1m6Cx9-009GeH-Ex; Wed, 21 Jul 2021 14:12:05 +0000 Date: Wed, 21 Jul 2021 15:12:03 +0100 From: Matthew Wilcox To: Mike Rapoport Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Christoph Hellwig Subject: Re: [PATCH v14 054/138] mm: Add kmap_local_folio() Message-ID: References: <20210715033704.692967-1-willy@infradead.org> <20210715033704.692967-55-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Authentication-Results: imf28.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=ZIkbTOln; spf=none (imf28.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org; dmarc=none X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: EF7B9900C53B X-Stat-Signature: mzgeicn6y19kjd7k9wsufz73dc66my94 X-HE-Tag: 1626876738-856305 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jul 21, 2021 at 12:58:24PM +0300, Mike Rapoport wrote: > > +/** > > + * kmap_local_folio - Map a page in this folio for temporary usage > > + * @folio: The folio to be mapped. > > + * @offset: The byte offset within the folio. > > + * > > + * Returns: The virtual address of the mapping > > + * > > + * Can be invoked from any context. > > Context: Can be invoked from any context. > > > + * > > + * Requires careful handling when nesting multiple mappings because the map > > + * management is stack based. The unmap has to be in the reverse order of > > + * the map operation: > > + * > > + * addr1 = kmap_local_folio(page1, offset1); > > + * addr2 = kmap_local_folio(page2, offset2); > > Please s/page/folio/g here and in the description below > > > + * ... > > + * kunmap_local(addr2); > > + * kunmap_local(addr1); > > + * > > + * Unmapping addr1 before addr2 is invalid and causes malfunction. > > + * > > + * Contrary to kmap() mappings the mapping is only valid in the context of > > + * the caller and cannot be handed to other contexts. > > + * > > + * On CONFIG_HIGHMEM=n kernels and for low memory pages this returns the > > + * virtual address of the direct mapping. Only real highmem pages are > > + * temporarily mapped. > > + * > > + * While it is significantly faster than kmap() for the higmem case it > > + * comes with restrictions about the pointer validity. Only use when really > > + * necessary. > > + * > > + * On HIGHMEM enabled systems mapping a highmem page has the side effect of > > + * disabling migration in order to keep the virtual address stable across > > + * preemption. No caller of kmap_local_folio() can rely on this side effect. > > + */ kmap_local_folio() only maps one page from the folio. So it's not appropriate to s/page/folio/g. I fiddled with the description a bit to make this clearer: /** * kmap_local_folio - Map a page in this folio for temporary usage - * @folio: The folio to be mapped. - * @offset: The byte offset within the folio. - * - * Returns: The virtual address of the mapping - * - * Can be invoked from any context. + * @folio: The folio containing the page. + * @offset: The byte offset within the folio which identifies the page. * * Requires careful handling when nesting multiple mappings because the map * management is stack based. The unmap has to be in the reverse order of * the map operation: * - * addr1 = kmap_local_folio(page1, offset1); - * addr2 = kmap_local_folio(page2, offset2); + * addr1 = kmap_local_folio(folio1, offset1); + * addr2 = kmap_local_folio(folio2, offset2); * ... * kunmap_local(addr2); * kunmap_local(addr1); @@ -131,6 +127,9 @@ static inline void *kmap_local_page(struct page *page); * On HIGHMEM enabled systems mapping a highmem page has the side effect of * disabling migration in order to keep the virtual address stable across * preemption. No caller of kmap_local_folio() can rely on this side effect. + * + * Context: Can be invoked from any context. + * Return: The virtual address of @offset. */ static inline void *kmap_local_folio(struct folio *folio, size_t offset);