Re: [PATCHv4] mm: skip CMA pages when they are not available

[Minchan Kim]

On Mon, May 22, 2023 at 02:36:03PM +0800, zhaoyang.huang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> 
> This patch fixes unproductive reclaiming of CMA pages by skipping them when they
> are not available for current context. It is arise from bellowing OOM issue, which
> caused by large proportion of MIGRATE_CMA pages among free pages.
> 
> [   36.172486] [03-19 10:05:52.172] ActivityManager: page allocation failure: order:0, mode:0xc00(GFP_NOIO), nodemask=(null),cpuset=foreground,mems_allowed=0
> [   36.189447] [03-19 10:05:52.189] DMA32: 0*4kB 447*8kB (C) 217*16kB (C) 124*32kB (C) 136*64kB (C) 70*128kB (C) 22*256kB (C) 3*512kB (C) 0*1024kB 0*2048kB 0*4096kB = 35848kB
> [   36.193125] [03-19 10:05:52.193] Normal: 231*4kB (UMEH) 49*8kB (MEH) 14*16kB (H) 13*32kB (H) 8*64kB (H) 2*128kB (H) 0*256kB 1*512kB (H) 0*1024kB 0*2048kB 0*4096kB = 3236kB
> ...
> [   36.234447] [03-19 10:05:52.234] SLUB: Unable to allocate memory on node -1, gfp=0xa20(GFP_ATOMIC)
> [   36.234455] [03-19 10:05:52.234] cache: ext4_io_end, object size: 64, buffer size: 64, default order: 0, min order: 0
> [   36.234459] [03-19 10:05:52.234] node 0: slabs: 53,objs: 3392, free: 0
> 
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> ---
> v2: update commit message and fix build error when CONFIG_CMA is not set
> v3,v4: update code and comments
> ---
> ---
>  mm/vmscan.c | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index bd6637f..20facec 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2193,6 +2193,26 @@ static __always_inline void update_lru_sizes(struct lruvec *lruvec,
>  
>  }
>  
> +#ifdef CONFIG_CMA
> +/*
> + * It is waste of effort to scan and reclaim CMA pages if it is not available
> + * for current allocation context
> + */
> +static bool skip_cma(struct folio *folio, struct scan_control *sc)
> +{
> +	if (!current_is_kswapd() &&

The function is called by isolate_lru_folios which is used by both background
and direct reclaims at the same time. And sc->reclaim_idx below to filter
unproductive reclaim out is used for both cases but why does the cma is considering
only direct reclaim path?


> +			gfp_migratetype(sc->gfp_mask) != MIGRATE_MOVABLE &&
> +			get_pageblock_migratetype(&folio->page) == MIGRATE_CMA)
> +		return true;
> +	return false;
> +}
> +#else
> +static bool skip_cma(struct folio *folio, struct scan_control *sc)
> +{
> +	return false;
> +}
> +#endif
> +
>  /*
>   * Isolating page from the lruvec to fill in @dst list by nr_to_scan times.
>   *
> @@ -2239,7 +2259,8 @@ static unsigned long isolate_lru_folios(unsigned long nr_to_scan,
>  		nr_pages = folio_nr_pages(folio);
>  		total_scan += nr_pages;
>  
> -		if (folio_zonenum(folio) > sc->reclaim_idx) {
> +		if (folio_zonenum(folio) > sc->reclaim_idx ||
> +				skip_cma(folio, sc)) {
>  			nr_skipped[folio_zonenum(folio)] += nr_pages;
>  			move_to = &folios_skipped;
>  			goto move;
> -- 
> 1.9.1
>