From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=a44y=DR=lists.ozlabs.org=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@kernel.org>
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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID,
	DKIM_SIGNED,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED
	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 98D35C43457
	for <linuxppc-dev@archiver.kernel.org>; Sat, 10 Oct 2020 01:33:01 +0000 (UTC)
Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
	(No client certificate requested)
	by mail.kernel.org (Postfix) with ESMTPS id EB516206D9
	for <linuxppc-dev@archiver.kernel.org>; Sat, 10 Oct 2020 01:33:00 +0000 (UTC)
Authentication-Results: mail.kernel.org;
	dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="kwaFsg+F"
DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EB516206D9
Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org
Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org
Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3])
	by lists.ozlabs.org (Postfix) with ESMTP id 4C7SB26YX7zDqwW
	for <linuxppc-dev@archiver.kernel.org>; Sat, 10 Oct 2020 12:32:58 +1100 (AEDT)
Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized)
 smtp.mailfrom=kernel.org (client-ip=198.145.29.99; helo=mail.kernel.org;
 envelope-from=ebiggers@kernel.org; receiver=<UNKNOWN>)
Authentication-Results: lists.ozlabs.org;
 dmarc=pass (p=none dis=none) header.from=kernel.org
Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key;
 unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256
 header.s=default header.b=kwaFsg+F; dkim-atps=neutral
Received: from mail.kernel.org (mail.kernel.org [198.145.29.99])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (No client certificate requested)
 by lists.ozlabs.org (Postfix) with ESMTPS id 4C7S7R1nk1zDqs6;
 Sat, 10 Oct 2020 12:30:43 +1100 (AEDT)
Received: from sol.localdomain (172-10-235-113.lightspeed.sntcca.sbcglobal.net
 [172.10.235.113])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (No client certificate requested)
 by mail.kernel.org (Postfix) with ESMTPSA id 4E006206D9;
 Sat, 10 Oct 2020 01:30:38 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org;
 s=default; t=1602293439;
 bh=sHFyDh52gnsvc+uI8yhUC5uDYbYkQCvra+rDiRMmAvs=;
 h=Date:From:To:Cc:Subject:References:In-Reply-To:From;
 b=kwaFsg+FwkcbT1hA6vX2rbzC7SEHg0ckV7q6+TfKUuTYp7lijGzsxhx1D9MfT9qZg
 puzd9VwNUhNC7pSZTswv9TmxeVvsyOKe33XMZMPqVG5rfdvIuh+YhVfWI5Z4mrkh0S
 V8+sp7izCEY2Jms4cmTCzh86mPIYz7uaZ6k3dzLQ=
Date: Fri, 9 Oct 2020 18:30:36 -0700
From: Eric Biggers <ebiggers@kernel.org>
To: Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH RFC PKS/PMEM 22/58] fs/f2fs: Utilize new kmap_thread()
Message-ID: <20201010013036.GD1122@sol.localdomain>
References: <20201009195033.3208459-1-ira.weiny@intel.com>
 <20201009195033.3208459-23-ira.weiny@intel.com>
 <20201009213434.GA839@sol.localdomain>
 <20201010003954.GW20115@casper.infradead.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20201010003954.GW20115@casper.infradead.org>
X-BeenThere: linuxppc-dev@lists.ozlabs.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Linux on PowerPC Developers Mail List <linuxppc-dev.lists.ozlabs.org>
List-Unsubscribe: <https://lists.ozlabs.org/options/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=unsubscribe>
List-Archive: <http://lists.ozlabs.org/pipermail/linuxppc-dev/>
List-Post: <mailto:linuxppc-dev@lists.ozlabs.org>
List-Help: <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=help>
List-Subscribe: <https://lists.ozlabs.org/listinfo/linuxppc-dev>,
 <mailto:linuxppc-dev-request@lists.ozlabs.org?subject=subscribe>
Cc: linux-aio@kvack.org, linux-efi@vger.kernel.org, kvm@vger.kernel.org,
 linux-doc@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>,
 linux-mmc@vger.kernel.org, Dave Hansen <dave.hansen@linux.intel.com>,
 dri-devel@lists.freedesktop.org, linux-mm@kvack.org,
 target-devel@vger.kernel.org, linux-mtd@lists.infradead.org,
 linux-kselftest@vger.kernel.org, ira.weiny@intel.com,
 Thomas Gleixner <tglx@linutronix.de>, drbd-dev@lists.linbit.com,
 devel@driverdev.osuosl.org, linux-cifs@vger.kernel.org,
 linux-nilfs@vger.kernel.org, linux-scsi@vger.kernel.org,
 linux-nvdimm@lists.01.org, linux-rdma@vger.kernel.org, x86@kernel.org,
 amd-gfx@lists.freedesktop.org, linux-afs@lists.infradead.org,
 cluster-devel@redhat.com, Ingo Molnar <mingo@redhat.com>,
 intel-wired-lan@lists.osuosl.org, kexec@lists.infradead.org,
 xen-devel@lists.xenproject.org, linux-ext4@vger.kernel.org,
 bpf@vger.kernel.org, Dan Williams <dan.j.williams@intel.com>,
 Fenghua Yu <fenghua.yu@intel.com>, intel-gfx@lists.freedesktop.org,
 ecryptfs@vger.kernel.org, linux-um@lists.infradead.org,
 reiserfs-devel@vger.kernel.org, linux-block@vger.kernel.org,
 linux-bcache@vger.kernel.org, Borislav Petkov <bp@alien8.de>,
 Andy Lutomirski <luto@kernel.org>, Jaegeuk Kim <jaegeuk@kernel.org>,
 ceph-devel@vger.kernel.org, io-uring@vger.kernel.org, linux-cachefs@redhat.com,
 linux-nfs@vger.kernel.org, linux-ntfs-dev@lists.sourceforge.net,
 netdev@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
 samba-technical@lists.samba.org, linux-kernel@vger.kernel.org,
 linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org,
 Andrew Morton <akpm@linux-foundation.org>, linux-erofs@lists.ozlabs.org,
 linux-btrfs@vger.kernel.org
Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org
Sender: "Linuxppc-dev"
 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>
Archived-At: <https://lore.kernel.org/linuxppc-dev/20201010013036.GD1122@sol.localdomain/>
List-Archive: <https://lore.kernel.org/linuxppc-dev/>

On Sat, Oct 10, 2020 at 01:39:54AM +0100, Matthew Wilcox wrote:
> On Fri, Oct 09, 2020 at 02:34:34PM -0700, Eric Biggers wrote:
> > On Fri, Oct 09, 2020 at 12:49:57PM -0700, ira.weiny@intel.com wrote:
> > > The kmap() calls in this FS are localized to a single thread.  To avoid
> > > the over head of global PKRS updates use the new kmap_thread() call.
> > >
> > > @@ -2410,12 +2410,12 @@ static inline struct page *f2fs_pagecache_get_page(
> > >  
> > >  static inline void f2fs_copy_page(struct page *src, struct page *dst)
> > >  {
> > > -	char *src_kaddr = kmap(src);
> > > -	char *dst_kaddr = kmap(dst);
> > > +	char *src_kaddr = kmap_thread(src);
> > > +	char *dst_kaddr = kmap_thread(dst);
> > >  
> > >  	memcpy(dst_kaddr, src_kaddr, PAGE_SIZE);
> > > -	kunmap(dst);
> > > -	kunmap(src);
> > > +	kunmap_thread(dst);
> > > +	kunmap_thread(src);
> > >  }
> > 
> > Wouldn't it make more sense to switch cases like this to kmap_atomic()?
> > The pages are only mapped to do a memcpy(), then they're immediately unmapped.
> 
> Maybe you missed the earlier thread from Thomas trying to do something
> similar for rather different reasons ...
> 
> https://lore.kernel.org/lkml/20200919091751.011116649@linutronix.de/

I did miss it.  I'm not subscribed to any of the mailing lists it was sent to.

Anyway, it shouldn't matter.  Patchsets should be standalone, and not require
reading random prior threads on linux-kernel to understand.

And I still don't really understand.  After this patchset, there is still code
nearly identical to the above (doing a temporary mapping just for a memcpy) that
would still be using kmap_atomic().  Is the idea that later, such code will be
converted to use kmap_thread() instead?  If not, why use one over the other?

- Eric