linux-ext4 - Re: [RFCv1 15/72] tst_bitmaps_pthread: Add merge bitmaps test using pthreads

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Message-Id: <AFE1174E-74AD-4EA3-ADFC-E7512BEC60AE@dilger.ca>
Date:   Wed, 14 Dec 2022 14:15:30 -0700
From:   Andreas Dilger <adilger@...ger.ca>
To:     "Ritesh Harjani (IBM)" <ritesh.list@...il.com>
Cc:     Theodore Ts'o <tytso@....edu>, linux-ext4@...r.kernel.org,
        Harshad Shirwadkar <harshadshirwadkar@...il.com>,
        Li Xi <lixi@....com>, Wang Shilong <wangshilong1991@...il.com>
Subject: Re: [RFCv1 15/72] tst_bitmaps_pthread: Add merge bitmaps test using
 pthreads

On Nov 7, 2022, at 5:21 AM, Ritesh Harjani (IBM) <ritesh.list@...il.com> wrote:
> 
> This patch adds a test to verify the core bitmaps merge APIs
> for rbtree bitmap type.
> 
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>

Reviewed-by: Andreas Dilger <adilger@...ger.ca>

> +/*
> + * Note we use EXT2FS_BMAP64_BITARRAY always for used_bitmap, this is because
> + * EXT2FS_BMAP64_RBTREE does not support parallel scan due to rcursor
> + * optimization.
> + */

Is this going to be a problem in the future?  I think for pass1/pass5 there
are no rbtree bitmaps that are *source* bitmaps for multi-threaded operation,
but I suspect that once we try to parallelize pass2 this could break.

Is there any check in the code that prevents multi-thread access to an rbtree
bitmap?  Making a copy for each thread, or ideally copying the rcursor for
each thread, to allow at least multi-threaded reads.  I don't think there is
a high need for multi-threaded write

Cheers, Andreas

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