linux-kernel - Re: [UPSTREAM KERNEL] mm/zsmalloc.c: Add module parameter malloc_force

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Date:   Wed, 29 May 2019 16:24:24 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Hui Zhu <teawaterz@...ux.alibaba.com>
Cc:     minchan@...nel.org, ngupta@...are.org,
        sergey.senozhatsky.work@...il.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [UPSTREAM KERNEL] mm/zsmalloc.c: Add module parameter
 malloc_force_movable

On (05/29/19 09:22), Hui Zhu wrote:
> When it enabled:
> ~# echo 1 > /sys/module/zsmalloc/parameters/malloc_force_movable
> ~# echo lz4 > /sys/module/zswap/parameters/compressor
> ~# echo zsmalloc > /sys/module/zswap/parameters/zpool
> ~# echo 1 > /sys/module/zswap/parameters/enabled
> ~# swapon /swapfile

[..]

>   * We assign a page to ZS_ALMOST_EMPTY fullness group when:
>   *	n <= N / f, where
> @@ -1479,6 +1486,9 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp)
>  	if (unlikely(!size || size > ZS_MAX_ALLOC_SIZE))
>  		return 0;
>  
> +	if (zs_malloc_force_movable)
> +		gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
> +
>  	handle = cache_alloc_handle(pool, gfp);
>  	if (!handle)
>  		return 0;

It's zsmalloc user's responsibility to pass appropriate GFP mask
to zs_malloc().

Take a loot at ZRAM, for instance,

	                handle = zs_malloc(zram->mem_pool, comp_len,
                                __GFP_KSWAPD_RECLAIM |
                                __GFP_NOWARN |
                                __GFP_HIGHMEM |
                                __GFP_MOVABLE);

zsmalloc should not change GFP. If zswap, for some reason,
doesn't pass __GFP_MOVABLE, then I'd suggest to patch zswap.

	-ss