linux-kernel - Re: [PATCH] mm: vmalloc: Refactor vm_area_alloc

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Message-ID: <ZtAtYAARL2gx8De5@pc636>
Date: Thu, 29 Aug 2024 10:12:16 +0200
From: Uladzislau Rezki <urezki@...il.com>
To: Baoquan He <bhe@...hat.com>
Cc: "Uladzislau Rezki (Sony)" <urezki@...il.com>, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Michal Hocko <mhocko@...e.com>,
	Oleksiy Avramchenko <oleksiy.avramchenko@...y.com>
Subject: Re: [PATCH] mm: vmalloc: Refactor vm_area_alloc_pages() function

On Thu, Aug 29, 2024 at 11:48:32AM +0800, Baoquan He wrote:
> On 08/27/24 at 09:09pm, Uladzislau Rezki (Sony) wrote:
> > The aim is to simplify and making the vm_area_alloc_pages()
> > function less confusing as it became more clogged nowadays:
> > 
> > - eliminate a "bulk_gfp" variable and do not overwrite a gfp
> >   flag for bulk allocator;
> > - drop __GFP_NOFAIL flag for high-order-page requests on upper
> >   layer. It becomes less spread between levels when it comes to
> >   __GFP_NOFAIL allocations;
> > - add a comment about a fallback path if high-order attempt is
> >   unsuccessful because for such cases __GFP_NOFAIL is dropped;
> > - fix a typo in a commit message.
> > 
> > Signed-off-by: Uladzislau Rezki (Sony) <urezki@...il.com>
> > ---
> >  mm/vmalloc.c | 37 +++++++++++++++++--------------------
> >  1 file changed, 17 insertions(+), 20 deletions(-)
> > 
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 3f9b6bd707d2..57862865e808 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -3531,8 +3531,6 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
> >  		unsigned int order, unsigned int nr_pages, struct page **pages)
> >  {
> >  	unsigned int nr_allocated = 0;
> > -	gfp_t alloc_gfp = gfp;
> > -	bool nofail = gfp & __GFP_NOFAIL;
> >  	struct page *page;
> >  	int i;
> >  
> > @@ -3543,9 +3541,6 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
> >  	 * more permissive.
> >  	 */
> >  	if (!order) {
> > -		/* bulk allocator doesn't support nofail req. officially */
> > -		gfp_t bulk_gfp = gfp & ~__GFP_NOFAIL;
> > -
> >  		while (nr_allocated < nr_pages) {
> >  			unsigned int nr, nr_pages_request;
> >  
> > @@ -3563,12 +3558,11 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
> >  			 * but mempolicy wants to alloc memory by interleaving.
> >  			 */
> >  			if (IS_ENABLED(CONFIG_NUMA) && nid == NUMA_NO_NODE)
> > -				nr = alloc_pages_bulk_array_mempolicy_noprof(bulk_gfp,
> > +				nr = alloc_pages_bulk_array_mempolicy_noprof(gfp,
> >  							nr_pages_request,
> >  							pages + nr_allocated);
> > -
> >  			else
> > -				nr = alloc_pages_bulk_array_node_noprof(bulk_gfp, nid,
> > +				nr = alloc_pages_bulk_array_node_noprof(gfp, nid,
> >  							nr_pages_request,
> >  							pages + nr_allocated);
> >  
> > @@ -3582,30 +3576,24 @@ vm_area_alloc_pages(gfp_t gfp, int nid,
> >  			if (nr != nr_pages_request)
> >  				break;
> >  		}
> > -	} else if (gfp & __GFP_NOFAIL) {
> > -		/*
> > -		 * Higher order nofail allocations are really expensive and
> > -		 * potentially dangerous (pre-mature OOM, disruptive reclaim
> > -		 * and compaction etc.
> > -		 */
> > -		alloc_gfp &= ~__GFP_NOFAIL;
> >  	}
> >  
> >  	/* High-order pages or fallback path if "bulk" fails. */
> >  	while (nr_allocated < nr_pages) {
> > -		if (!nofail && fatal_signal_pending(current))
> > +		if (!(gfp & __GFP_NOFAIL) && fatal_signal_pending(current))
> >  			break;
> >  
> >  		if (nid == NUMA_NO_NODE)
> > -			page = alloc_pages_noprof(alloc_gfp, order);
> > +			page = alloc_pages_noprof(gfp, order);
> >  		else
> > -			page = alloc_pages_node_noprof(nid, alloc_gfp, order);
> > +			page = alloc_pages_node_noprof(nid, gfp, order);
> > +
> >  		if (unlikely(!page))
> >  			break;
> >  
> >  		/*
> >  		 * Higher order allocations must be able to be treated as
> > -		 * indepdenent small pages by callers (as they can with
> > +		 * independent small pages by callers (as they can with
> >  		 * small-page vmallocs). Some drivers do their own refcounting
> >  		 * on vmalloc_to_page() pages, some use page->mapping,
> >  		 * page->lru, etc.
> > @@ -3666,7 +3654,16 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
> >  	set_vm_area_page_order(area, page_shift - PAGE_SHIFT);
> >  	page_order = vm_area_page_order(area);
> >  
> > -	area->nr_pages = vm_area_alloc_pages(gfp_mask | __GFP_NOWARN,
> > +	/*
> > +	 * Higher order nofail allocations are really expensive and
>            ~~~~~~~~~~~~
> Seems we use both higher-order and high-order to describe the
> non 0-order pages in many places. I personally would take high-order,
> higher-order seems to be a little confusing because it's not explicit
> what is compared with and lower.
> 
> Surely this is not an issue to this patch, I see a lot of 'higher order'
> in kernel codes.
> 
I agree. It sounds like hard to figure out the difference between both.
Are you willing send the patch? If not, i can send it out :)

> For this patch,
> 
> Reviewed-by: Baoquan He <bhe@...hat.com>
> 
Thanks!

--
Uladzislau Rezki