linux-kernel - Re: [PATCH v3 1/7] mm/vmalloc.c: add used_map into vmap_block to track space of vmap

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Date:   Mon, 16 Jan 2023 12:22:08 +0000
From:   Lorenzo Stoakes <lstoakes@...il.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org, urezki@...il.com,
        stephen.s.brennan@...cle.com, willy@...radead.org,
        akpm@...ux-foundation.org, hch@...radead.org
Subject: Re: [PATCH v3 1/7] mm/vmalloc.c: add used_map into vmap_block to
 track space of vmap_block

On Fri, Jan 13, 2023 at 11:19:15AM +0800, Baoquan He wrote:
> In one vmap_block area, there could be three types of regions: region
> being used which is allocated through vb_alloc(), dirty region which
> is freed via vb_free() and free region. Among them, only used region
> has available data. While there's no way to track those used regions
> currently.
>
> Here, add bitmap field used_map into vmap_block, and set/clear it during
> allocation or freeing regions of vmap_block area.
>
> This is a preparatoin for later use.
>
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
>  mm/vmalloc.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 428e0bee5c9c..d6ff058ef4d0 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1922,6 +1922,7 @@ struct vmap_block {
>  	spinlock_t lock;
>  	struct vmap_area *va;
>  	unsigned long free, dirty;
> +	DECLARE_BITMAP(used_map, VMAP_BBMAP_BITS);
>  	unsigned long dirty_min, dirty_max; /*< dirty range */
>  	struct list_head free_list;
>  	struct rcu_head rcu_head;
> @@ -1998,10 +1999,12 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask)
>  	vb->va = va;
>  	/* At least something should be left free */
>  	BUG_ON(VMAP_BBMAP_BITS <= (1UL << order));
> +	bitmap_zero(vb->used_map, VMAP_BBMAP_BITS);
>  	vb->free = VMAP_BBMAP_BITS - (1UL << order);
>  	vb->dirty = 0;
>  	vb->dirty_min = VMAP_BBMAP_BITS;
>  	vb->dirty_max = 0;
> +	bitmap_set(vb->used_map, 0, (1UL << order));
>  	INIT_LIST_HEAD(&vb->free_list);
>
>  	vb_idx = addr_to_vb_idx(va->va_start);
> @@ -2111,6 +2114,7 @@ static void *vb_alloc(unsigned long size, gfp_t gfp_mask)
>  		pages_off = VMAP_BBMAP_BITS - vb->free;
>  		vaddr = vmap_block_vaddr(vb->va->va_start, pages_off);
>  		vb->free -= 1UL << order;
> +		bitmap_set(vb->used_map, pages_off, (1UL << order));
>  		if (vb->free == 0) {
>  			spin_lock(&vbq->lock);
>  			list_del_rcu(&vb->free_list);
> @@ -2144,6 +2148,9 @@ static void vb_free(unsigned long addr, unsigned long size)
>  	order = get_order(size);
>  	offset = (addr & (VMAP_BLOCK_SIZE - 1)) >> PAGE_SHIFT;
>  	vb = xa_load(&vmap_blocks, addr_to_vb_idx(addr));
> +	spin_lock(&vb->lock);
> +	bitmap_clear(vb->used_map, offset, (1UL << order));
> +	spin_unlock(&vb->lock);
>
>  	vunmap_range_noflush(addr, addr + size);
>
> --
> 2.34.1
>

Reviewed-by: Lorenzo Stoakes <lstoakes@...il.com>