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Fri, 9 Oct 2020 19:43:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=hansenpartnership.com; s=20151216; t=1602297796; bh=H8TP93foEqN1ktQ8Zvn50X/i2mF1Mo+G3bAPl3laMS8=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=BgjiThamK3sRChTIWem3VqlcTVcZOY3Z2GNJyIwpezgtDJLGW3IszUxOTE+yoCAWv V48K29iXWIdEyZfVjEsU0FSlh3cTrvJt0EqAPo1Ll9Jsfhk5OlUorelNGWOoKpuPOj SS1Y94jSiSEug+8lBRnZGZxsf1hZ1ZG8/+ovIeYw= Message-ID: <95d137992900152a0453f7ba37771cb9025121fa.camel@HansenPartnership.com> Subject: Re: [PATCH RFC PKS/PMEM 22/58] fs/f2fs: Utilize new kmap_thread() From: James Bottomley To: Eric Biggers , ira.weiny@intel.com Cc: 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 Date: Fri, 09 Oct 2020 19:43:13 -0700 In-Reply-To: <20201009213434.GA839@sol.localdomain> References: <20201009195033.3208459-1-ira.weiny@intel.com> <20201009195033.3208459-23-ira.weiny@intel.com> <20201009213434.GA839@sol.localdomain> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.34.4 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Fri, 2020-10-09 at 14:34 -0700, Eric Biggers wrote: > On Fri, Oct 09, 2020 at 12:49:57PM -0700, ira.weiny@intel.com wrote: > > From: Ira Weiny > > > > 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. > > > > Cc: Jaegeuk Kim > > Cc: Chao Yu > > Signed-off-by: Ira Weiny > > --- > > fs/f2fs/f2fs.h | 8 ++++---- > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h > > index d9e52a7f3702..ff72a45a577e 100644 > > --- a/fs/f2fs/f2fs.h > > +++ b/fs/f2fs/f2fs.h > > @@ -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. On a VIPT/VIVT architecture, this is horrendously wasteful. You're taking something that was mapped at colour c_src mapping it to a new address src_kaddr, which is likely a different colour and necessitates flushing the original c_src, then you copy it to dst_kaddr, which is also likely a different colour from c_dst, so dst_kaddr has to be flushed on kunmap and c_dst has to be invalidated on kmap. What we should have is an architectural primitive for doing this, something like kmemcopy_arch(dst, src). PIPT architectures can implement it as the above (possibly losing kmap if they don't need it) but VIPT/VIVT architectures can set up a correctly coloured mapping so they can simply copy from c_src to c_dst without any need to flush and the data arrives cache hot at c_dst. James