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

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Message-ID: <Zs/vkLWrRNRkSvwC@MiWiFi-R3L-srv>
Date: Thu, 29 Aug 2024 11:48:32 +0800
From: Baoquan He <bhe@...hat.com>
To: "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc: 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 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.

For this patch,

Reviewed-by: Baoquan He <bhe@...hat.com>

> +	 * potentially dangerous (pre-mature OOM, disruptive reclaim
> +	 * and compaction etc.
> +	 *
> +	 * Please note, the __vmalloc_node_range_noprof() falls-back
> +	 * to order-0 pages if high-order attempt is unsuccessful.
> +	 */
> +	area->nr_pages = vm_area_alloc_pages((page_order ?
> +		gfp_mask & ~__GFP_NOFAIL : gfp_mask) | __GFP_NOWARN,
>  		node, page_order, nr_small_pages, area->pages);
>  
>  	atomic_long_add(area->nr_pages, &nr_vmalloc_pages);
> -- 
> 2.39.2
>