linux-kernel - Re: [RESEND PATCH v1] mm/vmalloc: fix page mapping if vm_area_alloc_pages() with high order fallback to order 0

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Message-ID: <20240819125738.vbjlw3qbv2v2rj57@oppo.com>
Date: Mon, 19 Aug 2024 20:57:38 +0800
From: Hailong Liu <hailong.liu@...o.com>
To: Uladzislau Rezki <urezki@...il.com>
CC: Michal Hocko <mhocko@...e.com>, Andrew Morton <akpm@...ux-foundation.org>,
	Barry Song <21cnbao@...il.com>, Christoph Hellwig <hch@...radead.org>,
	Vlastimil Babka <vbabka@...e.cz>, Tangquan Zheng <zhengtangquan@...o.com>,
	<stable@...r.kernel.org>, Baoquan He <bhe@...hat.com>, Matthew Wilcox
	<willy@...radead.org>, <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND PATCH v1] mm/vmalloc: fix page mapping if
 vm_area_alloc_pages() with high order fallback to order 0

On Mon, 19. Aug 13:59, Uladzislau Rezki wrote:
> On Fri, Aug 16, 2024 at 07:46:26PM +0800, Hailong Liu wrote:
> > On Fri, 16. Aug 12:13, Uladzislau Rezki wrote:
> > > On Fri, Aug 16, 2024 at 05:12:32PM +0800, Hailong Liu wrote:
> > > > On Thu, 15. Aug 22:07, Andrew Morton wrote:
> > > > > On Fri, 9 Aug 2024 11:41:42 +0200 Uladzislau Rezki <urezki@...il.com> wrote:
> > > > >
> > > > > > > > Acked-by: Barry Song <baohua@...nel.org>
> > > > > > > >
> > > > > > > > because we already have a fallback here:
> > > > > > > >
> > > > > > > > void *__vmalloc_node_range_noprof :
> > > > > > > >
> > > > > > > > fail:
> > > > > > > >         if (shift > PAGE_SHIFT) {
> > > > > > > >                 shift = PAGE_SHIFT;
> > > > > > > >                 align = real_align;
> > > > > > > >                 size = real_size;
> > > > > > > >                 goto again;
> > > > > > > >         }
> > > > > > >
> > > > > > > This really deserves a comment because this is not really clear at all.
> > > > > > > The code is also fragile and it would benefit from some re-org.
> > > > > > >
> > > > > > > Thanks for the fix.
> > > > > > >
> > > > > > > Acked-by: Michal Hocko <mhocko@...e.com>
> > > > > > >
> > > > > > I agree. This is only clear for people who know the code. A "fallback"
> > > > > > to order-0 should be commented.
> > > > >
> > > > > It's been a week.  Could someone please propose a fixup patch to add
> > > > > this comment?
> > > >
> > > > Hi Andrew:
> > > >
> > > > Do you mean that I need to send a v2 patch with the the comments included?
> > > >
> > > It is better to post v2.
> > Got it.
> >
> > >
> > > But before, could you please comment on:
> > >
> > > in case of order-0, bulk path may easily fail and fallback to the single
> > > page allocator. If an request is marked as NO_FAIL, i am talking about
> > > order-0 request, your change breaks GFP_NOFAIL for !order.
> > >
> > > Am i missing something obvious?
> > For order-0, alloc_pages(GFP_X | __GFP_NOFAIL, 0), buddy allocator will handle
> > the flag correctly. IMO we don't need to handle the flag here.
> >
> Agree. As for comment, i meant to comment the below fallback:
Michal send a craft that make nofail logic more clearer and I check the branch
found Andrew already merged in -stable branch. So we can include these with a
new patch.
>
> <snip>
> fail:
> 	if (shift > PAGE_SHIFT) {
> 		shift = PAGE_SHIFT;
> 		align = real_align;
> 		size = real_size;
> 		goto again;
> 	}
> <snip>
>
> --
> Uladzislau Rezki

--

Help you, Help me,
Hailong.