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From: Yang Shi <shy828301@gmail.com>
Date: Mon, 5 Feb 2024 09:07:16 -0800
Message-ID: <CAHbLzkp7s1CcSE0rc-CpfcCrNtMdepAA5-K+0P4wz11x4SK6=g@mail.gmail.com>
Subject: Re: [PATCH] mm: huge_memory: don't force huge page alignment on 32 bit
To: Thorsten Leemhuis <regressions@leemhuis.info>
Cc: jirislaby@kernel.org, surenb@google.com, riel@surriel.com, 
	willy@infradead.org, cl@linux.com, akpm@linux-foundation.org, 
	Linux kernel regressions list <regressions@lists.linux.dev>, yang@os.amperecomputing.com, 
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
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On Sat, Feb 3, 2024 at 1:24=E2=80=AFAM Thorsten Leemhuis
<regressions@leemhuis.info> wrote:
>
> On 18.01.24 14:35, Yang Shi wrote:
> > From: Yang Shi <yang@os.amperecomputing.com>
> >
> > The commit efa7df3e3bb5 ("mm: align larger anonymous mappings on THP
> > boundaries") caused two issues [1] [2] reported on 32 bit system or com=
pat
> > userspace.
> >
> > 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
>
> [FWIW, this is now 4ef9ad19e17676 ("mm: huge_memory: don't force huge
> page alignment on 32 bit") in mainline]
>
> Quick question: it it okay to ask Greg to pick this up for linux-6.7.y
> series?

Yes, definitely. Thanks for following up.

Yang

>
> I'm wondering because Jiri's report ([1] in above quote) sounded like
> this is something that will affect and annoy quite a few people with the
> linux-6.7.y.
>
> Ciao, Thorsten
>
> > Fixes: efa7df3e3bb5 ("mm: align larger anonymous mappings on THP bounda=
ries")
> > Reported-by: Jiri Slaby <jirislaby@kernel.org>
> > Reported-by: Suren Baghdasaryan <surenb@google.com>
> > Tested-by: Jiri Slaby <jirislaby@kernel.org>
> > Tested-by: Suren Baghdasaryan <surenb@google.com>
> > Cc: Rik van Riel <riel@surriel.com>
> > Cc: Matthew Wilcox <willy@infradead.org>
> > Cc: Christopher Lameter <cl@linux.com>
> > Signed-off-by: Yang Shi <yang@os.amperecomputing.com>
> > ---
> >  mm/huge_memory.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index 94ef5c02b459..e9fbaccbe0c0 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -37,6 +37,7 @@
> >  #include <linux/page_owner.h>
> >  #include <linux/sched/sysctl.h>
> >  #include <linux/memory-tiers.h>
> > +#include <linux/compat.h>
> >
> >  #include <asm/tlb.h>
> >  #include <asm/pgalloc.h>
> > @@ -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.
> > +      */
> > +     if (IS_ENABLED(CONFIG_32BIT) || in_compat_syscall())
> > +             return 0;
> > +
> >       if (off_end <=3D off_align || (off_end - off_align) < size)
> >               return 0;
> >