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Thu, 18 Jan 2024 12:40:07 -0800 (PST) MIME-Version: 1.0 References: <20240118133504.2910955-1-shy828301@gmail.com> In-Reply-To: From: Yang Shi Date: Thu, 18 Jan 2024 12:39:55 -0800 Message-ID: Subject: Re: [PATCH] mm: huge_memory: don't force huge page alignment on 32 bit To: Matthew Wilcox Cc: jirislaby@kernel.org, surenb@google.com, riel@surriel.com, cl@linux.com, akpm@linux-foundation.org, yang@os.amperecomputing.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 22B0D40002 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: 8xgd9u5k7jaw5tofkcitnxnba9ychfjw X-HE-Tag: 1705610408-399612 X-HE-Meta: U2FsdGVkX1/QejJ2gTen9/YY8xBZZJd6xfdMdrMqrsbNd7hLaZBi3iR9VU7wUDJzvS/gqiw+rnqeuKZx6uk73MhdnQD0uJ587VNwvl17bm2djRaW3mf1ll7Asc6P5hLPsQG5Vh3IG5fm2t9L2w3kd3kIa5N4PbPtj0lpJDqm4xJOdI6DKHZsr8MjVSe9+ZcMdC89MMrqB3Uz8oY9D3WtrI6AgNfwD66f27OpDrWmrxr0rKMsad08czo3YlwAZKEx1Z2NBUp54viSrPTKvuoSIXh145ep3GsnpHnZDt3De+gCyfUKgTQMO4pJrVIAUOFnCXaaF9jGvMEqo/mtfM3TY59P9hqjUhoR0ewfm7R2JycNKB/RR1PSGjDHIX6ea6Gf9IgyG1RzqYrKPXJLj4g9lUuGomU1GArxlAxmkoVom1u5gSW+nGbOeaaKNX4N6hPT24TcLwQnSs5m54fiNbcxA29oNyJVTVOixM8gk2Bo1kxVclVYTxApuSVjIEivnVxdLsX9a4dMZgRLE5oSrVCN6cN+gVQBirW+r2eutWADveOUvwudSiEWsfkRsfn78MjH6KIaeivqjyeiGRzMGkIZ5HNq4igcRX27g29Vz3T1YJDTKdxy2NChtaU8wRv/gjXPuBej69xNg6Xcs48aS4wjhXaBVJV0TO9wUbKxXhaHERdC1kFD9PYNx1VlOZRYH3dDx8Nr/wEtfPqvy6zhxLlsRpuDjiMlTBSwjLRXqjwjW/TO9/SutkMqmzCQejRZfrx+qKNHFZqd16wyEkQp2/i4f9VZn6y1oGvpNq5Fok+JkBw2dfdubRC8PIiDqjZs+QLN81y9M0P5nHRH7TeVNnVgqda3uTwH6BIHDn4Nxd7VNWgkEAx05PYxcUYS+tKoBTBl608/l6QyUileflsSYTozqkcYsEJrKrLGRusemLhnt7eI4xpnTOUIq60gfv3Pg5mQFdIuZiCZYoVZh8uhCuh EGekPqnL 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000236, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jan 18, 2024 at 12:14=E2=80=AFPM Matthew Wilcox wrote: > > On Thu, Jan 18, 2024 at 05:35:04AM -0800, Yang Shi wrote: > > It doesn't make too much sense to force huge page alignment on 32 bit > > system due to the constrained virtual address space. > > > > [1] https://lore.kernel.org/linux-mm/CAHbLzkqa1SCBA10yjWTtA2mKCsoK5+M1B= thSDL8ROvUq2XxZMw@mail.gmail.com/T/#mf211643a0427f8d6495b5b53f8132f453d60ab= 95 > > [2] https://lore.kernel.org/linux-mm/CAHbLzkqa1SCBA10yjWTtA2mKCsoK5+M1B= thSDL8ROvUq2XxZMw@mail.gmail.com/T/#me93dff2ccbd9902c3e395e1c022fb454e48ecb= 1d > > I feel sure there are shorter URLs for those messages ... Oh, yeah, I just found. [1] https://lore.kernel.org/linux-mm/d0a136a0-4a31-46bc-adf4-2db109a61672@k= ernel.org/ [2] https://lore.kernel.org/linux-mm/CAJuCfpHXLdQy1a2B6xN2d7quTYwg2OoZseYPZ= TRpU0eHHKD-sQ@mail.gmail.com/ > > > @@ -811,6 +812,14 @@ static unsigned long __thp_get_unmapped_area(struc= t file *filp, > > loff_t off_align =3D round_up(off, size); > > unsigned long len_pad, ret; > > > > + /* > > + * It doesn't make too much sense to froce huge page alignment on > > + * 32 bit system or compat userspace due to the contrained virtua= l > > + * address space and address entropy. > > + */ > > I honestly wouldn't even comment this. But if you must, > > /* Using THP alignment is not as important as address randomisati= on */ It is not only about address randomization. Removing the comment is fine to= o. > > > + if (IS_ENABLED(CONFIG_32BIT) || in_compat_syscall()) > > + return 0; > > + > > if (off_end <=3D off_align || (off_end - off_align) < size) > > return 0; > > > > -- > > 2.41.0 > >