linux-kernel - Re: [RFC PATCH v2] mm/vmalloc: fix incorrect __vmap_pages_range_noflush() if vm_area_alloc_pages() from high order fallback to order0

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Message-ID: <20240725095826.pqt4shyiw6odgcem@oppo.com>
Date: Thu, 25 Jul 2024 17:58:26 +0800
From: Hailong Liu <hailong.liu@...o.com>
To: Barry Song <21cnbao@...il.com>
CC: Andrew Morton <akpm@...ux-foundation.org>, Uladzislau Rezki
	<urezki@...il.com>, Christoph Hellwig <hch@...radead.org>, Lorenzo Stoakes
	<lstoakes@...il.com>, Vlastimil Babka <vbabka@...e.cz>, Michal Hocko
	<mhocko@...e.com>, Baoquan He <bhe@...hat.com>, Matthew Wilcox
	<willy@...radead.org>, "Tangquan . Zheng" <zhengtangquan@...o.com>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2] mm/vmalloc: fix incorrect
 __vmap_pages_range_noflush() if vm_area_alloc_pages() from high order
 fallback to order0

On Thu, 25. Jul 21:34, Barry Song wrote:
> On Thu, Jul 25, 2024 at 9:17 PM Hailong Liu <hailong.liu@...o.com> wrote:
> >
> > On Thu, 25. Jul 18:21, Barry Song wrote:
> > > On Thu, Jul 25, 2024 at 3:53 PM <hailong.liu@...o.com> wrote:
> > [snip]
> > >
> > > This is still incorrect because it undoes Michal's work. We also need to break
> > > the loop if (!nofail), which you're currently omitting.
> >
> > IIUC, the origin issue is to fix kvcalloc with __GFP_NOFAIL return NULL.
> > https://lore.kernel.org/all/ZAXynvdNqcI0f6Us@dhcp22.suse.cz/T/#u
> > if we disable huge flag in kmalloc_node, the issue will be fixed.
>
> No, this just bypasses kvmalloc and doesn't solve the underlying issue. Problems
> can still be triggered by vmalloc_huge() even after the bypass. Once we
> reorganize vmap_huge to support the combination of PMD and PTE
> mapping, we should re-enable HUGE_VMAP for kvmalloc.
Totally agree, This will take some time to support. As in [1] I prepare to fix
with a offset in page_private to indicate the location of fallback.

>
> I would consider dropping VM_ALLOW_HUGE_VMAP() for kvmalloc as
> an short-term "optimization" to save memory rather than a long-term fix. This
> 'optimization' is only valid until we reorganize HUGE_VMAP in a way
> similar to THP. I mean, for a 2.1MB kvmalloc, we can map 2MB as PMD
> and 0.1 as PTE.
However this just fixed the kvmalloc_node, but for others who call
vmalloc_huge(), the issue exits. so I remove the Michal's code. sorry for this.

>
> > >
> > > To avoid reverting Michal's work, the simplest "fix" would be,
> > >
> > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > > index caf032f0bd69..0011ca30df1c 100644
> > > --- a/mm/vmalloc.c
> > > +++ b/mm/vmalloc.c
> > > @@ -3775,7 +3775,7 @@ void *__vmalloc_node_range_noprof(unsigned long
> > > size, unsigned long align,
> > >                 return NULL;
> > >         }
> > >
> > > -       if (vmap_allow_huge && (vm_flags & VM_ALLOW_HUGE_VMAP)) {
> > > +       if (vmap_allow_huge && (vm_flags & VM_ALLOW_HUGE_VMAP) &
> > > !(gfp_mask & __GFP_NOFAIL)) {
> > >                 unsigned long size_per_node;
> > >
> > >                 /*
> > > >
> > > > [1] https://lore.kernel.org/lkml/20240724182827.nlgdckimtg2gwns5@oppo.com/
> > > > 2.34.1
> > >
> > > Thanks
> > > Barry
> >
> > --
> > help you, help me,
> > Hailong.

--
help you, help me,
Hailong.