linux-ext4 - Re: [PATCH 10/37] mke2fs: Allow metadata checksums to be turned on at mkfs time

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Date:	Mon, 5 Sep 2011 12:20:27 -0700
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Andreas Dilger <adilger@...ger.ca>
Cc:	Andreas Dilger <adilger.kernel@...ger.ca>,
	Theodore Tso <tytso@....edu>,
	Sunil Mushran <sunil.mushran@...cle.com>,
	Amir Goldstein <amir73il@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Mingming Cao <cmm@...ibm.com>,
	Joel Becker <jlbec@...lplan.org>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	Coly Li <colyli@...il.com>
Subject: Re: [PATCH 10/37] mke2fs: Allow metadata checksums to be turned on
	at mkfs time

On Sun, Sep 04, 2011 at 12:28:24PM -0600, Andreas Dilger wrote:
> On 2011-08-31, at 6:36 PM, "Darrick J. Wong" <djwong@...ibm.com> wrote:
> > Write out checksummed inodes even when writing out a zeroed table.
> > 
> > Signed-off-by: Darrick J. Wong <djwong@...ibm.com>
> > ---
> > misc/mke2fs.c |   37 ++++++++++++++++++++++++++++++-------
> > 1 files changed, 30 insertions(+), 7 deletions(-)
> > 
> > 
> > diff --git a/misc/mke2fs.c b/misc/mke2fs.c
> > index 2d57d09..bbc0533 100644
> > --- a/misc/mke2fs.c
> > +++ b/misc/mke2fs.c
> > @@ -309,6 +309,8 @@ static void write_inode_tables(ext2_filsys fs, int lazy_flag, int itable_zeroed)
> >    dgrp_t        i;
> >    int        num;
> >    struct ext2fs_numeric_progress_struct progress;
> > +    ext2_ino_t    ino;
> > +    struct ext2_inode_large inode;
> > 
> >    ext2fs_numeric_progress_init(fs, &progress,
> >                     _("Writing inode tables: "),
> > @@ -330,12 +332,32 @@ static void write_inode_tables(ext2_filsys fs, int lazy_flag, int itable_zeroed)
> >            ext2fs_bg_flags_set(fs, i, EXT2_BG_INODE_ZEROED);
> >            ext2fs_group_desc_csum_set(fs, i);
> >        }
> > -        retval = ext2fs_zero_blocks2(fs, blk, num, &blk, &num);
> > -        if (retval) {
> > -            fprintf(stderr, _("\nCould not write %d "
> > -                  "blocks in inode table starting at %llu: %s\n"),
> > -                num, blk, error_message(retval));
> > -            exit(1);
> > +        if (fs->super->s_creator_os == EXT2_OS_LINUX &&
> > +            fs->super->s_feature_ro_compat &
> > +            EXT4_FEATURE_RO_COMPAT_METADATA_CSUM) {
> 
> Somehow it doesn't look like this is skipping the zeroing of the inode table
> blocks if lazy itable zeroing is set. 
> 
> Any measurements on how much this slows down inode table writing (which is
> already the slowest part of mke2fs)?

Quite a lot, actually.  Trouble is, if you're going to write zeroes to the
inode table (without using uninit) then I think you need the checksums to
match.  Maybe the solution is to modify the kernel/e2fsck to ignore the
checksum if the inode bitmap says the inode isn't in use?

A better solution is to zero the buffer, stuff in all the checksums in the
correct places, and then write the block out.

> > +            bzero(&inode, sizeof(inode));
> > +            for (ino = fs->super->s_inodes_per_group * i;
> > +                 ino < fs->super->s_inodes_per_group * (i + 1);
> > +                 ino++) {
> 
> Why recompute "ino" each time through this loop?  It should be enough to
> simply initialize it at 1 and then increment it for each inode written. 

Agreed.

--D
> > +                if (!ino)
> > +                    continue;
> > +                retval = ext2fs_write_inode(fs, ino, &inode);
> > +                if (retval) {
> > +                    com_err("inode_init", retval,
> > +                        "while writing inode %d\n",
> > +                        ino);
> > +                    exit(1);
> > +                }
> > +            }
> > +        } else {
> > +            retval = ext2fs_zero_blocks2(fs, blk, num, &blk, &num);
> > +            if (retval) {
> > +                fprintf(stderr, _("\nCould not write %d "
> > +                    "blocks in inode table starting "
> > +                    "at %llu: %s\n"),
> > +                    num, blk, error_message(retval));
> > +                exit(1);
> > +            }
> >        }
> >        if (sync_kludge) {
> >            if (sync_kludge == 1)
> > @@ -829,7 +851,8 @@ static __u32 ok_features[3] = {
> >        EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE|
> >        EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER|
> >        EXT4_FEATURE_RO_COMPAT_GDT_CSUM|
> > -        EXT4_FEATURE_RO_COMPAT_BIGALLOC
> > +        EXT4_FEATURE_RO_COMPAT_BIGALLOC|
> > +        EXT4_FEATURE_RO_COMPAT_METADATA_CSUM
> > };
> > 
> > 
> > 
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