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Sat, 10 Oct 2020 01:30:40 +0000 (UTC) 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 To: Matthew Wilcox Cc: ira.weiny@intel.com, Andrew Morton , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Andy Lutomirski , Peter Zijlstra , linux-aio@kvack.org, linux-efi@vger.kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-mmc@vger.kernel.org, Dave Hansen , dri-devel@lists.freedesktop.org, linux-mm@kvack.org, target-devel@vger.kernel.org, linux-mtd@lists.infradead.org, linux-kselftest@vger.kernel.org, samba-technical@lists.samba.org, ceph-devel@vger.kernel.org, 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, linux-cachefs@redhat.com, intel-wired-lan@lists.osuosl.org, xen-devel@lists.xenproject.org, linux-ext4@vger.kernel.org, Fenghua Yu , ecryptfs@vger.kernel.org, linux-um@lists.infradead.org, intel-gfx@lists.freedesktop.org, linux-erofs@lists.ozlabs.org, reiserfs-devel@vger.kernel.org, linux-block@vger.kernel.org, linux-bcache@vger.kernel.org, Jaegeuk Kim , Dan Williams , io-uring@vger.kernel.org, linux-nfs@vger.kernel.org, linux-ntfs-dev@lists.sourceforge.net, netdev@vger.kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-fsdevel@vger.kernel.org, bpf@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-btrfs@vger.kernel.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-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 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