linux-kernel - Re: [PATCH 1/2] mm/page_alloc: Ensure try_alloc_pages() plays well with unaccepted memory

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Message-ID: <ruyfdyo7hfb3bdlcfhi4quphrupdyy225flao2xre5vlz5rnbz@ixr26npbzydd>
Date: Wed, 7 May 2025 14:13:45 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	Vlastimil Babka <vbabka@...e.cz>, Suren Baghdasaryan <surenb@...gle.com>, 
	Michal Hocko <mhocko@...e.com>, Brendan Jackman <jackmanb@...gle.com>, 
	Johannes Weiner <hannes@...xchg.org>, Borislav Petkov <bp@...en8.de>, 
	Thomas Gleixner <tglx@...utronix.de>, David Hildenbrand <david@...hat.com>, 
	Alexei Starovoitov <ast@...nel.org>, linux-mm <linux-mm@...ck.org>, linux-coco@...ts.linux.dev, 
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm/page_alloc: Ensure try_alloc_pages() plays well
 with unaccepted memory

On Tue, May 06, 2025 at 03:05:31PM -0700, Alexei Starovoitov wrote:
> On Tue, May 6, 2025 at 12:00 PM Kirill A. Shutemov
> <kirill.shutemov@...ux.intel.com> wrote:
> >
> > On Tue, May 06, 2025 at 10:18:21AM -0700, Alexei Starovoitov wrote:
> > > On Tue, May 6, 2025 at 4:25 AM Kirill A. Shutemov
> > > <kirill.shutemov@...ux.intel.com> wrote:
> > > >
> > > > try_alloc_pages() will not attempt to allocate memory if the system has
> > > > *any* unaccepted memory. Memory is accepted as needed and can remain in
> > > > the system indefinitely, causing the interface to always fail.
> > > >
> > > > Rather than immediately giving up, attempt to use already accepted
> > > > memory on free lists.
> > > >
> > > > Pass 'alloc_flags' to cond_accept_memory() and do not accept new memory
> > > > for ALLOC_TRYLOCK requests.
> > > >
> > > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > > > Fixes: 97769a53f117 ("mm, bpf: Introduce try_alloc_pages() for opportunistic page allocation")
> > >
> > > Thanks for working on this, but the fixes tag is overkill.
> > > This limitation is not causing any issues in our setups.
> >
> > Have you had chance to test it on any platform with unaccepted memory?
> > So far it is only Intel TDX and AMD SEV guests.
> 
> We don't use them, and my understanding is that such
> unaccepted memory will be there only during boot time.

That's false. Unaccepted memory can be there indefinitely after boot. It
only gets accepted on demand.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov