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

[Jiri Slaby]

On 25. 01. 24, 9:53, Michal Hocko wrote:
> On Thu 18-01-24 05:35:04, Yang Shi wrote:
> > From: Yang Shi <yang@xxxxxxxxxxxxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxxxx/T/#mf211643a0427f8d6495b5b53f8132f453d60ab95
> > [2] https://lore.kernel.org/linux-mm/CAHbLzkqa1SCBA10yjWTtA2mKCsoK5+M1BthSDL8ROvUq2XxZMw@xxxxxxxxxxxxxx/T/#me93dff2ccbd9902c3e395e1c022fb454e48ecb1d
> >
> > Fixes: efa7df3e3bb5 ("mm: align larger anonymous mappings on THP boundaries")
> > Reported-by: Jiri Slaby <jirislaby@xxxxxxxxxx>
> > Reported-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> > Tested-by: Jiri Slaby <jirislaby@xxxxxxxxxx>
> > Tested-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> > Cc: Rik van Riel <riel@xxxxxxxxxxx>
> > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> > Cc: Christopher Lameter <cl@xxxxxxxxx>
> > Signed-off-by: Yang Shi <yang@xxxxxxxxxxxxxxxxxxxxxx>
>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
>
> Thanks!
>
> > ---
> >   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.
> > +	 */

FWIW,
Bernhard noticed that "froce" and "contrained", could you fix that 
before applying the patch?

thanks,
--
js
suse labs