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

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Date: Mon, 5 Feb 2024 09:07:16 -0800
From: Yang Shi <shy828301@...il.com>
To: Thorsten Leemhuis <regressions@...mhuis.info>
Cc: jirislaby@...nel.org, surenb@...gle.com, riel@...riel.com, 
	willy@...radead.org, cl@...ux.com, akpm@...ux-foundation.org, 
	Linux kernel regressions list <regressions@...ts.linux.dev>, yang@...amperecomputing.com, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: huge_memory: don't force huge page alignment on 32 bit

On Sat, Feb 3, 2024 at 1:24 AM Thorsten Leemhuis
<regressions@...mhuis.info> wrote:
>
> On 18.01.24 14:35, Yang Shi wrote:
> > From: Yang Shi <yang@...amperecomputing.com>
> >
> > The commit efa7df3e3bb5 ("mm: align larger anonymous mappings on THP
> > boundaries") caused two issues [1] [2] reported on 32 bit system or compat
> > 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+M1BthSDL8ROvUq2XxZMw@mail.gmail.com/T/#mf211643a0427f8d6495b5b53f8132f453d60ab95
> > [2] https://lore.kernel.org/linux-mm/CAHbLzkqa1SCBA10yjWTtA2mKCsoK5+M1BthSDL8ROvUq2XxZMw@mail.gmail.com/T/#me93dff2ccbd9902c3e395e1c022fb454e48ecb1d
>
> [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 boundaries")
> > Reported-by: Jiri Slaby <jirislaby@...nel.org>
> > Reported-by: Suren Baghdasaryan <surenb@...gle.com>
> > Tested-by: Jiri Slaby <jirislaby@...nel.org>
> > Tested-by: Suren Baghdasaryan <surenb@...gle.com>
> > Cc: Rik van Riel <riel@...riel.com>
> > Cc: Matthew Wilcox <willy@...radead.org>
> > Cc: Christopher Lameter <cl@...ux.com>
> > Signed-off-by: Yang Shi <yang@...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(struct file *filp,
> >       loff_t off_align = 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 virtual
> > +      * address space and address entropy.
> > +      */
> > +     if (IS_ENABLED(CONFIG_32BIT) || in_compat_syscall())
> > +             return 0;
> > +
> >       if (off_end <= off_align || (off_end - off_align) < size)
> >               return 0;
> >