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Date: Sun, 3 May 2020 22:04:47 -0700 From: Ira Weiny <ira.weiny@...el.com> To: Al Viro <viro@...iv.linux.org.uk> Cc: linux-kernel@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>, Christian Koenig <christian.koenig@....com>, Huang Rui <ray.huang@....com>, Thomas Bogendoerfer <tsbogend@...ha.franken.de>, "James E.J. Bottomley" <James.Bottomley@...senpartnership.com>, Helge Deller <deller@....de>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Paul Mackerras <paulus@...ba.org>, "David S. Miller" <davem@...emloft.net>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Chris Zankel <chris@...kel.net>, Max Filippov <jcmvbkbc@...il.com>, Dan Williams <dan.j.williams@...el.com>, linux-snps-arc@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org, linux-csky@...r.kernel.org, linux-mips@...r.kernel.org, linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, sparclinux@...r.kernel.org, linux-xtensa@...ux-xtensa.org, dri-devel@...ts.freedesktop.org Subject: Re: [PATCH V2 00/11] Subject: Remove duplicated kmap code On Mon, May 04, 2020 at 02:35:09AM +0100, Al Viro wrote: > On Sun, May 03, 2020 at 06:09:01PM -0700, ira.weiny@...el.com wrote: > > From: Ira Weiny <ira.weiny@...el.com> > > > > The kmap infrastructure has been copied almost verbatim to every architecture. > > This series consolidates obvious duplicated code by defining core functions > > which call into the architectures only when needed. > > > > Some of the k[un]map_atomic() implementations have some similarities but the > > similarities were not sufficient to warrant further changes. > > > > In addition we remove a duplicate implementation of kmap() in DRM. > > > > Testing was done by 0day to cover all the architectures I can't readily > > build/test. > > OK... Looking through my old notes on kmap unification (this winter, never > went anywhere), > > * arch/mips/mm/cache.c ought to use linux/highmem.h, not asm/highmem.h > I suspect that your series doesn't build on some configs there. Hadn't > verified that, though. Yes patch 6 makes the change because kmap_atomic() was no longer declared in asm/highmem.h. I'm pretty sure 0-day caught that ... but I seem to remember noticing some oddness in that file and I did go through it by hand. > > * kmap_atomic_to_page() is dead, but not quite gone - csky and nds32 brought > the damn thing back (nds32 - only an extern). It needs killin'... Easy enough. Added as a follow on patch. > > * parisc is (arguably) abusing kunmap()/kunmap_atomic() for cache flushing. > Replace the bulk of its highmem.h with > #define ARCH_HAS_FLUSH_ON_KUNMAP > #define arch_before_kunmap flush_kernel_dcache_page_addr > and have default kunmap()/kunmap_atomic() do > #ifdef ARCH_HAS_FLUSH_ON_KUNMAP > arch_before_kunmap(page_address(page)); > #endif > and > #ifdef ARCH_HAS_FLUSH_ON_KUNMAP > arch_before_kunmap(addr); > #endif > resp. Kills ARCH_HAS_KMAP along with ifdefs on it, makes parisc use somewhat > less hacky. Agreed. Done in a follow on patch. > > I'd suggest checking various configs on mips - that's likely to cause headache. > Said that, my analysis of include chains back then is pretty much worthless > by now - I really hate the amount of indirect include chains leading to that > sucker on some, but not all configs ;-/ IIRC, the proof that everything > using kmap*/kunmap* would pull linux/highmem.h regardless of config took several > hours of digging, ran for several pages and had been hopelessly brittle. > arch/mips/mm/cache.c was the only exception caught by it, but these days > there might be more. Grepping for 'asm/highmem.h' and investigations don't reveal any issues... But you do have me worried. That said 0-day has been crunching on multiple versions of this series without issues such as this (save the mips issue above). I have to say it would be nice if the relation between linux/highmem.h and asm/highmem.h was more straightforward. Ira
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