linux-kernel - Re: [PATCH] mm: huge_memory: don't force huge page alignment on 32 bit

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Message-ID: <ZpFAt6ha2KbFRoFn@corsac.net>
Date: Fri, 12 Jul 2024 16:41:59 +0200
From: Yves-Alexis Perez <corsac@...ian.org>
To: Yang Shi <shy828301@...il.com>
Cc: Matthew Wilcox <willy@...radead.org>, jirislaby@...nel.org,
	surenb@...gle.com, riel@...riel.com, cl@...ux.com,
	akpm@...ux-foundation.org, yang@...amperecomputing.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Salvatore Bonaccorso <carnil@...ian.org>,
	Ben Hutchings <ben@...adent.org.uk>
Subject: Re: [PATCH] mm: huge_memory: don't force huge page alignment on 32
 bit

On Thu, Jul 11, 2024 at 01:53:04PM -0700, Yang Shi wrote:
> On Thu, Jul 11, 2024 at 1:50 PM Matthew Wilcox <willy@...radead.org> wrote:
> >
> > On Thu, Jul 11, 2024 at 01:47:00PM -0700, Yang Shi wrote:
> > > +++ b/mm/huge_memory.c
> > > @@ -857,7 +857,8 @@ static unsigned long
> > > __thp_get_unmapped_area(struct file *filp,
> > >         loff_t off_align = round_up(off, size);
> > >         unsigned long len_pad, ret, off_sub;
> > >
> > > -       if (IS_ENABLED(CONFIG_32BIT) || in_compat_syscall())
> > > +       if (IS_ENABLED(CONFIG_32BIT) || IS_ENABLED(CONFIG_X86_32) ||
> > > +           in_compat_syscall())
> >
> > Why not:
> >
> >         if (!IS_ENABLED(CONFIG_64BIT) || in_compat_syscall())
> 
> Nothing specific, just didn't think of it, sigh...
> 
> Thanks for the suggestion. Definitely preferable way.
> 
And I just did a quick test rebuilding a kernel with
!IS_ENABLED(CONFIG_64BIT) and running on an i386 Debian sid
installation.

I can confirm it seems to work as intended:

Before:
root@...tvm:~# uname -a
Linux testvm 6.9.8-686-pae #1 SMP PREEMPT_DYNAMIC Debian 6.9.8-1 (2024-07-07) i686 GNU/Linux
root@...tvm:~# for i in {0..9}; do cat /proc/self/maps |grep libc.so |head -n1; done
b7c00000-b7c22000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7c00000-b7c22000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7c00000-b7c22000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7c00000-b7c22000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7c00000-b7c22000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7c00000-b7c22000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7c00000-b7c22000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7c00000-b7c22000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7c00000-b7c22000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7c00000-b7c22000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6


After:

root@...tvm:~# uname -a
Linux testvm 6.9.8+ #1 SMP PREEMPT_DYNAMIC Fri Jul 12 15:23:07 CEST 2024 i686 GNU/Linux
root@...tvm:~# for i in {0..9}; do cat /proc/self/maps |grep libc.so |head -n1; done
b7cf3000-b7d15000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7d7a000-b7d9c000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7d8b000-b7dad000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7d4b000-b7d6d000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7d64000-b7d86000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7d15000-b7d37000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7c9e000-b7cc0000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7d68000-b7d8a000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7cf6000-b7d18000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6
b7ce6000-b7d08000 r--p 00000000 fe:00 933        /usr/lib/i386-linux-gnu/libc.so.6

So:
Tested-By: Yves-Alexis Perez <corsac@...ian.org>

I didn't try on other 32b architectures though.

Regards,
-- 
Yves-Alexis Perez