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Shutemov" Cc: Steven Price , Mark Rutland , Dave Hansen , Arnd Bergmann , Ard Biesheuvel , Peter Zijlstra , Catalin Marinas , x86@kernel.org, Will Deacon , linux-kernel@vger.kernel.org, linux-mm@kvack.org, =?iso-8859-1?B?Suly9G1l?= Glisse , Ingo Molnar , Borislav Petkov , Andy Lutomirski , "H. Peter Anvin" , James Morse , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, "Liang, Kan" Subject: Re: [PATCH v2 03/13] mm: Add generic p?d_large() macros References: <20190221113502.54153-1-steven.price@arm.com> <20190221113502.54153-4-steven.price@arm.com> <20190221142812.oa53lfnnfmsuh6ys@kshutemo-mobl1> <20190221145706.zqwfdoyiirn3lc7y@kshutemo-mobl1> <20190221210618.voyfs5cnafpvgedh@kshutemo-mobl1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190221210618.voyfs5cnafpvgedh@kshutemo-mobl1> User-Agent: Mutt/1.5.24 (2015-08-30) X-TM-AS-GCONF: 00 x-cbid: 19030111-0016-0000-0000-0000025C7989 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19030111-0017-0000-0000-000032B6ED0A Message-Id: <20190301115300.GE5156@rapoport-lnx> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-03-01_09:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=936 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1903010084 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: Him Kirill, On Fri, Feb 22, 2019 at 12:06:18AM +0300, Kirill A. Shutemov wrote: > On Thu, Feb 21, 2019 at 05:16:46PM +0000, Steven Price wrote: > > >> Note that in terms of the new page walking code, these new defines are > > >> only used when walking a page table without a VMA (which isn't currently > > >> done), so architectures which don't use p?d_large currently will work > > >> fine with the generic versions. They only need to provide meaningful > > >> definitions when switching to use the walk-without-a-VMA functionality. > > > > > > How other architectures would know that they need to provide the helpers > > > to get walk-without-a-VMA functionality? This looks very fragile to me. > > > > Yes, you've got a good point there. This would apply to the p?d_large > > macros as well - any arch which (inadvertently) uses the generic version > > is likely to be fragile/broken. > > > > I think probably the best option here is to scrap the generic versions > > altogether and simply introduce a ARCH_HAS_PXD_LARGE config option which > > would enable the new functionality to those arches that opt-in. Do you > > think this would be less fragile? > > These helpers are useful beyond pagewalker. > > Can we actually do some grinding and make *all* archs to provide correct > helpers? Yes, it's tedious, but not that bad. Many architectures simply cannot support non-leaf entries at the higher levels. I think letting the use a generic helper actually does make sense. > I think we could provide generic helpers for folded levels in > and rest has to be provided by the arch. > Architectures that support only 2 level paging would need to provide > pgd_large(), with 3 -- pmd_large() and so on. > > -- > Kirill A. Shutemov -- Sincerely yours, Mike.