linux-kernel - Re: [RFC PATCH v1] 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: <ZqFdu73H3BguX4QG@casper.infradead.org>
Date: Wed, 24 Jul 2024 21:02:03 +0100
From: Matthew Wilcox <willy@...radead.org>
To: "Hailong.Liu" <hailong.liu@...o.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>,
	Barry Song <21cnbao@...il.com>,
	"Tangquan . Zheng" <zhengtangquan@...o.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1] mm/vmalloc: fix incorrect
 __vmap_pages_range_noflush() if vm_area_alloc_pages() from high order
 fallback to order0

On Thu, Jul 25, 2024 at 02:28:27AM +0800, Hailong.Liu wrote:
> >  	if (!IS_ENABLED(CONFIG_HAVE_ARCH_HUGE_VMALLOC) ||
> > -			page_shift == PAGE_SHIFT)
> > -		return vmap_small_pages_range_noflush(addr, end, prot, pages);
> > +			page_shift == PAGE_SHIFT ||
> > +			page_private(pages[0]) == VM_AREA_ALLOC_PAGES_FALLBACK) {
> > +		int ret = vmap_small_pages_range_noflush(addr, end, prot, pages);
> > +
> > +		set_page_private(pages[0], 0);
> > +		return ret;
> > +	}
> >
> >  	for (i = 0; i < nr; i += 1U << (page_shift - PAGE_SHIFT)) {
> >  		int err;
> > @@ -3583,6 +3590,7 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
> >
> >  			/* fall back to the zero order allocations */
> >  			alloc_gfp |= __GFP_NOFAIL;
> > +			fallback = true;
> Sry for my mistake, I forget define fallback here.
> BTW, This is not the optimal solution. Does anyone have a better idea? Glad to
> hear:)

Yeah, I really don't like this approach.  You could return a small
struct indicating both nr_allocated and whether you had to fall back.
Or you could pass a bool * parameter.  They're both pretty nasty.