linux-kernel - Re: [PATCH v3 2/7] mm/vmalloc.c: add flags to mark vm_map

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Date:   Mon, 16 Jan 2023 12:42:32 +0100
From:   Uladzislau Rezki <urezki@...il.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org, urezki@...il.com,
        lstoakes@...il.com, stephen.s.brennan@...cle.com,
        willy@...radead.org, akpm@...ux-foundation.org, hch@...radead.org
Subject: Re: [PATCH v3 2/7] mm/vmalloc.c: add flags to mark vm_map_ram area

On Fri, Jan 13, 2023 at 11:19:16AM +0800, Baoquan He wrote:
> Through vmalloc API, a virtual kernel area is reserved for physical
> address mapping. And vmap_area is used to track them, while vm_struct
> is allocated to associate with the vmap_area to store more information
> and passed out.
> 
> However, area reserved via vm_map_ram() is an exception. It doesn't have
> vm_struct to associate with vmap_area. And we can't recognize the
> vmap_area with '->vm == NULL' as a vm_map_ram() area because the normal
> freeing path will set va->vm = NULL before unmapping, please see
> function remove_vm_area().
> 
> Meanwhile, there are two kinds of handling for vm_map_ram area. One is
> the whole vmap_area being reserved and mapped at one time through
> vm_map_area() interface; the other is the whole vmap_area with
> VMAP_BLOCK_SIZE size being reserved, while mapped into split regions
> with smaller size via vb_alloc().
> 
> To mark the area reserved through vm_map_ram(), add flags field into
> struct vmap_area. Bit 0 indicates this is vm_map_ram area created
> through vm_map_ram() interface, while bit 1 marks out the type of
> vm_map_ram area which makes use of vmap_block to manage split regions
> via vb_alloc/free().
> 
> This is a preparatoin for later use.
> 
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
>  include/linux/vmalloc.h |  1 +
>  mm/vmalloc.c            | 16 ++++++++++++----
>  2 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index 096d48aa3437..69250efa03d1 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -76,6 +76,7 @@ struct vmap_area {
>  		unsigned long subtree_max_size; /* in "free" tree */
>  		struct vm_struct *vm;           /* in "busy" tree */
>  	};
> +	unsigned long flags; /* mark type of vm_map_ram area */
>  };
>  
>  /* archs that select HAVE_ARCH_HUGE_VMAP should override one or more of these */
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index d6ff058ef4d0..ab4825050b5c 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1589,7 +1589,8 @@ preload_this_cpu_lock(spinlock_t *lock, gfp_t gfp_mask, int node)
>  static struct vmap_area *alloc_vmap_area(unsigned long size,
>  				unsigned long align,
>  				unsigned long vstart, unsigned long vend,
> -				int node, gfp_t gfp_mask)
> +				int node, gfp_t gfp_mask,
> +				unsigned long va_flags)
>  {
>  	struct vmap_area *va;
>  	unsigned long freed;
> @@ -1635,6 +1636,7 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
>  	va->va_start = addr;
>  	va->va_end = addr + size;
>  	va->vm = NULL;
> +	va->flags = va_flags;
>  
>  	spin_lock(&vmap_area_lock);
>  	insert_vmap_area(va, &vmap_area_root, &vmap_area_list);
> @@ -1913,6 +1915,10 @@ static struct vmap_area *find_unlink_vmap_area(unsigned long addr)
>  
>  #define VMAP_BLOCK_SIZE		(VMAP_BBMAP_BITS * PAGE_SIZE)
>  
> +#define VMAP_RAM		0x1 /* indicates vm_map_ram area*/
> +#define VMAP_BLOCK		0x2 /* mark out the vmap_block sub-type*/
> +#define VMAP_FLAGS_MASK		0x3
> +
>  struct vmap_block_queue {
>  	spinlock_t lock;
>  	struct list_head free;
> @@ -1988,7 +1994,8 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask)
>  
>  	va = alloc_vmap_area(VMAP_BLOCK_SIZE, VMAP_BLOCK_SIZE,
>  					VMALLOC_START, VMALLOC_END,
> -					node, gfp_mask);
> +					node, gfp_mask,
> +					VMAP_RAM|VMAP_BLOCK);
>  	if (IS_ERR(va)) {
>  		kfree(vb);
>  		return ERR_CAST(va);
> @@ -2297,7 +2304,8 @@ void *vm_map_ram(struct page **pages, unsigned int count, int node)
>  	} else {
>  		struct vmap_area *va;
>  		va = alloc_vmap_area(size, PAGE_SIZE,
> -				VMALLOC_START, VMALLOC_END, node, GFP_KERNEL);
> +				VMALLOC_START, VMALLOC_END,
> +				node, GFP_KERNEL, VMAP_RAM);
>  		if (IS_ERR(va))
>  			return NULL;
>  
> @@ -2537,7 +2545,7 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
>  	if (!(flags & VM_NO_GUARD))
>  		size += PAGE_SIZE;
>  
> -	va = alloc_vmap_area(size, align, start, end, node, gfp_mask);
> +	va = alloc_vmap_area(size, align, start, end, node, gfp_mask, 0);
>  	if (IS_ERR(va)) {
>  		kfree(area);
>  		return NULL;
> -- 
> 2.34.1
> 
Reviewed-by: Uladzislau Rezki (Sony) <urezki@...il.com>

--
Uladzislau Rezki