linux-kernel - Re: [PATCH 2/3] mm/vmalloc: Switch to bulk allocator in __vmalloc_area

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Date:   Wed, 19 May 2021 14:44:08 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     "Uladzislau Rezki (Sony)" <urezki@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...e.de>,
        Matthew Wilcox <willy@...radead.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Hillf Danton <hdanton@...a.com>,
        Michal Hocko <mhocko@...e.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 2/3] mm/vmalloc: Switch to bulk allocator in
 __vmalloc_area_node()

> +	if (!page_order) {
> +		area->nr_pages = alloc_pages_bulk_array_node(
> +			gfp_mask, node, nr_small_pages, area->pages);
> +	} else {
> +		/*
> +		 * Careful, we allocate and map page_order pages, but tracking is done
> +		 * per PAGE_SIZE page so as to keep the vm_struct APIs independent of

Comments over 80 lines are completely unreadable, so please avoid them.

> +		 * the physical/mapped size.
> +		 */
> +		while (area->nr_pages < nr_small_pages) {
> +			struct page *page;
> +			int i;
> +
> +			/* Compound pages required for remap_vmalloc_page */
> +			page = alloc_pages_node(node, gfp_mask | __GFP_COMP, page_order);
> +			if (unlikely(!page))
> +				break;
>  
> +			for (i = 0; i < (1U << page_order); i++)
> +				area->pages[area->nr_pages + i] = page + i;
>  
> +			if (gfpflags_allow_blocking(gfp_mask))
> +				cond_resched();
> +
> +			area->nr_pages += 1U << page_order;
> +		}

In fact splitting this whole high order allocation logic into a little
helper would massivel benefit the function by ordering it more logical
and reducing a level of indentation.

> +	/*
> +	 * If not enough pages were obtained to accomplish an
> +	 * allocation request, free them via __vfree() if any.
> +	 */
> +	if (area->nr_pages != nr_small_pages) {
> +		warn_alloc(gfp_mask, NULL,
> +			"vmalloc size %lu allocation failure: "
> +			"page order %u allocation failed",
> +			area->nr_pages * PAGE_SIZE, page_order);
> +		goto fail;
> +	}

>From reading __alloc_pages_bulk not allocating all pages is something
that cn happen fairly easily.  Shouldn't we try to allocate the missing
pages manually and/ore retry here?

> +
> +	if (vmap_pages_range(addr, addr + size, prot, area->pages, page_shift) < 0) {

Another pointlessly long line.