Re: [PATCH] mm/zblock: use vmalloc for page allocations

[Johannes Weiner <hannes@cmpxchg.org>]

On Fri, May 02, 2025 at 10:01:56AM +0200, Vitaly Wool wrote:
>  static struct zblock_block *alloc_block(struct zblock_pool *pool,
>  					int block_type, gfp_t gfp,
> -					unsigned long *handle)
> +					unsigned long *handle,
> +					unsigned int nid)
>  {
> +	struct block_list *block_list = &pool->block_lists[block_type];
> +	unsigned int num_pages = block_desc[block_type].num_pages;
>  	struct zblock_block *block;
> -	struct block_list *block_list;
> +	struct page *page = NULL;
>  
> -	block = (void *)__get_free_pages(gfp, block_desc[block_type].order);
> -	if (!block)
> -		return NULL;
> +	if (!vmalloc_small_blocks && zblock_get_order(num_pages) >= 0) {
> +		page = try_alloc_pages(nid, zblock_get_order(num_pages));

This is broken in several ways.

The function is meant for NMI contexts - the "try" refers to
trylocking the freelists, in case whatever got interrupted was inside
the allocator already. This will fall back to vmalloc unpredictably.

It also doesn't take a gfp parameter, which ignores the zswap ones,
and substitutes a set that doesn't make any sense in this context:
__GFP_NOMEMALLOC is counter productive inside reclaim; __GFP_ACCOUNT
wreaks complete havoc on how compressed memory is charged to cgroups
(double charging the wrong groups for shared blocks).