linux-ext4 - Re: [PATCH 2/3] Add batched discard support for ext3

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Date:	Wed, 4 Aug 2010 13:39:28 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	linux-ext4@...r.kernel.org, jmoyer@...hat.com, rwheeler@...hat.com,
	eshishki@...hat.com, sandeen@...hat.com, jack@...e.cz,
	tytso@....edu
Subject: Re: [PATCH 2/3] Add batched discard support for ext3

On 2010-08-04, at 07:44, Lukas Czerner wrote:
> +		/*
> +		 * Clear bits in the bitmap
> +		 */
> +		for (bit = start; bit < next; bit++) {
> +			BUFFER_TRACE(bitmap_bh, "clear bit");
> +			if (!ext3_clear_bit_atomic(sb_bgl_lock(sbi, group),
> +						bit, bitmap_bh->b_data)) {
> +				ext3_error(sb, __func__,
> +					"bit already cleared for block "E3FSBLK,
> +					 (unsigned long)bit);
> +				BUFFER_TRACE(bitmap_bh, "bit already cleared");
> +			} else {
> +				freed++;
> +			}
> +		}
> +
> +		/* Update couters */
> +		spin_lock(sb_bgl_lock(sbi, group));
> +		le16_add_cpu(&gdp->bg_free_blocks_count, freed);
> +		spin_unlock(sb_bgl_lock(sbi, group));
> +		percpu_counter_add(&sbi->s_freeblocks_counter, next - start);

It wouldn't be a terrible idea to put this code into a helper function that is shared with ext3_free_blocks_sb() so that it is kept in sync.  There are a lot of places that need to be kept coordinated (disk bitmap, memory bitmap, group descriptor, percpu counter) so I'd like that to be localized to one part of the code.


Cheers, Andreas





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