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: <Zs7ObXBgULkuvaXK@tiehlicka>
Date: Wed, 28 Aug 2024 09:14:53 +0200
From: Michal Hocko <mhocko@...e.com>
To: Uladzislau Rezki <urezki@...il.com>
Cc: Hailong Liu <hailong.liu@...o.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 Tue 27-08-24 17:29:34, Uladzislau Rezki wrote:
> On Tue, Aug 27, 2024 at 03:37:38PM +0200, Michal Hocko wrote:
> > On Tue 27-08-24 14:47:30, Uladzislau Rezki wrote:
> > > On Tue, Aug 26, 2024 at 08:49:35AM +0200, Michal Hocko wrote:
> > [...]
> > > > > 2. High-order allocations. Do you think we should not care much about
> > > > > it when __GFP_NOFAIL is set? Same here, there is a fallback for order-0
> > > > > if "high" fails, it is more likely NO_FAIL succeed for order-0. Thus
> > > > > keeping NOFAIL for high-order sounds like not a good approach to me.
> > > > 
> > > > We should avoid high order allocations with GFP_NOFAIL at all cost.
> > > > 
> > > What do you propose here? Fail such request?
> > 
> > We shouldn't have any hard requirements for higher order allocations in the vmalloc
> > right? In other words we can always fallback to base pages.
> >
> We always drop NOFAIL for high-order, if it fails we fall-back to
> order-0. I got the feeling that you wanted just bail-out fully if
> high-order and NOFAIL.

Nope. We should always fall back to order 0 for both NOFAIL and regular
vmalloc allocations.

-- 
Michal Hocko
SUSE Labs