linux-kernel - Re: [PATCH 2/6] writeback: support retrieving per group debug writeback stats of bdi

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Date: Tue, 26 Mar 2024 13:24:21 +0100
From: Jan Kara <jack@...e.cz>
To: Kemeng Shi <shikemeng@...weicloud.com>
Cc: akpm@...ux-foundation.org, tj@...nel.org, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	willy@...radead.org, bfoster@...hat.com, jack@...e.cz,
	dsterba@...e.com, mjguzik@...il.com, dhowells@...hat.com,
	peterz@...radead.org
Subject: Re: [PATCH 2/6] writeback: support retrieving per group debug
 writeback stats of bdi

On Wed 20-03-24 19:02:18, Kemeng Shi wrote:
> Add /sys/kernel/debug/bdi/xxx/wb_stats to show per group writeback stats
> of bdi.
> 
> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>

..

> +unsigned long wb_calc_cg_thresh(struct bdi_writeback *wb)
> +{
> +	struct dirty_throttle_control gdtc = { GDTC_INIT_NO_WB };
> +	struct dirty_throttle_control mdtc = { MDTC_INIT(wb, &gdtc) };
> +	unsigned long filepages, headroom, writeback;
> +
> +	gdtc.avail = global_dirtyable_memory();
> +	gdtc.dirty = global_node_page_state(NR_FILE_DIRTY) +
> +		     global_node_page_state(NR_WRITEBACK);
> +
> +	mem_cgroup_wb_stats(wb, &filepages, &headroom,
> +			    &mdtc.dirty, &writeback);
> +	mdtc.dirty += writeback;
> +	mdtc_calc_avail(&mdtc, filepages, headroom);
> +	domain_dirty_limits(&mdtc);
> +
> +	return __wb_calc_thresh(&mdtc, mdtc.thresh);
> +}

I kind of wish we didn't replicate this logic from balance_dirty_pages()
and wb_over_bg_thresh() into yet another place. But the refactoring would
be kind of difficult. So OK.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR