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Shutemov" , Guenter Roeck , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm-treewide-redefine-max_order-sanely-fix.txt Message-Id: <20230406154423.20a991bbdd47630fc38d94e8@linux-foundation.org> In-Reply-To: References: <9460377a-38aa-4f39-ad57-fb73725f92db@roeck-us.net> <20230406072529.vupqyrzqnhyozeyh@box.shutemov.name> <83e6bc46-dfc0-0e95-e69c-5b996af1e50b@roeck-us.net> <20230406151015.yndcm24fyxitvqyc@box.shutemov.name> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: EDACC1A0004 X-Stat-Signature: wasuhnyrsy61xdnbhndsyfdg9nzfa615 X-HE-Tag: 1680821065-726120 X-HE-Meta: U2FsdGVkX19LbeTqzpVzASDLrSQBL8YFlJSTv14BtMmudtPoI/YElEockr7oHD7zloUjb0ckp6FVZ1E4Q6r6b4ZNvvHyfOrcLEr520vBp1IRXX3BgTocCrXVCRRQGTjbBibhskYgIR4X611sVF8QvxXONhBNlnGWsnelusLcfBWievED46ggypP1HIOFc/UxIehq8qOikXmd0nieDOgXepHzM5HDIfy6vHb5xjo5uFkN7ottXeHnkQeDlQ7KEEM3YrGsbJTMrZQ3vHhue3qxmbkQ43eZ7Cfb+0RXrtg3KzdZPjpy7Xe5C/V80L4YWlLbgajrAzINZ4JLkJaVfNVAVVWhJ/UoBtpstSjzAFua6m02nXmjjVMMjeZv+Z44ClN4vxr/JB8E5qg9tfjsCw6ENm7b3Xx0h7cBJzcZrPxIbrMTmq09BkGe2ZT5o/OolfupB+iqExOAHpHOaP6+JzKubernUv1hDfSENBy93JZBidyIGnuKC8KtazVFtU8O58P6aBT5G49L9H1G9bQOkw8Os0B9QBVFdGyGHkJ7OJW3aZtryunSR4P02awMaRBCbVovrRt/hEQYBe/SNnSGZaAV38XlZRL0d3yjBpYh/ZGhBIur0FDKR0+r6vBFDT1npmlvF72OFbqbmVgiW3iuBYylRSrP8srt1rgJBeztnRZK4lJZIyfbi3mAjXgFo2seO40zjGru/c+p1hCikCCtvEkYxEdCcZ6a0elbVbMo+IX+4iaG4qLDYbnepItaVSbmJEK267Fs8mVo+QS8Mj+4vRk8fJXOAxRah8k0A+T+eEY5dx5KqOii3zqAo7/ZGKOEZ/kJ9ndYxLYBmOOBV6h8lH4Gsn00yVREO9kmQT2HGevOtAqm3AKpM/QWeLSd+6pB4YZVjPEnIFBgBRMflDxHQRMrOaO6ux0dUiKcSDCjZI5/Uc2hABCX+5MrfjwcUjro/PPy9+z1j+M7AaC4tefWjJC IW5f6aBA +tbh6Ys1TxNTbY5xo+Qmqh4Xn444ORl+ph1BjbjMGMLfcP7DRJWMcOr2N4h8gJ2UQG7TeIXUywd2lvMjHC34igei4b3pjKVtHbIOdvzG71Yj5VdCOocT4dyfjzhRmI4gqNKHVaSua3rpBXJ2Sj7x+wY3TEgMEm0fDV37KthOgZPPyJKk9S04+5bAdvpsZUC5sb6ikNNOLWT9ZtI2GBuUrEFbKoK0zN2iSYjZghJvCh7/DYS3zD0lwBBtCM1LpSSpYbYXDxVaFif5/+u/Q4MPAEZqO5NpY/hR/wtj6p/rvjAg27vLSJr2l6dGyHkIT36WRVFAEuFAtKYqjYXlL4c6wtQKptByL5/V2HDd3lDQ8+XK9DFO0sPFJgT0DuzgDvJT4Nab1BkLGjBYQjS64EoeEFx8K7jhfAl29hvA2QTeWZAMHpapHLH5tKCFWZt1Oo/0TTnvn 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 Fri, 7 Apr 2023 00:14:31 +0300 Mike Rapoport wrote: > > > Shouldn't that be > > > else > > > order = 0; > > > ? > > > > +Mike. > > > > No. start == 0 is MAX_ORDER-aligned. We want to free the pages in the > > largest chunks alignment allows. > > Right. Before the changes to MAX_ORDER it was > > order = min(MAX_ORDER - 1UL, __ffs(start)); > > which would evaluate to 10. > > I'd just prefer the comment to include the explanation about why we choose > MAX_ORDER for start == 0. Say > > /* > * __ffs() behaviour is undefined for 0 and we want to free the > * pages in the largest chunks alignment allows, so set order to > * MAX_ORDER when start == 0 > */ Meanwhile I'd like to fix "various boot failures (hang) on arm targets" in -next, so I queued up Kirill's informal fix for now.