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From: David Sterba <dsterba@suse.cz>
To: Timofey Titovets <nefelim4ag@gmail.com>
Cc: David Sterba <dsterba@suse.cz>,
	linux-btrfs <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH 4/4] [RESEND] Btrfs: reduce size of struct btrfs_inode
Date: Tue, 1 May 2018 17:39:45 +0200	[thread overview]
Message-ID: <20180501153945.GW21272@twin.jikos.cz> (raw)
In-Reply-To: <CAGqmi75LLs9T9HEJQEx53HMKCvHPjM7jDKPBELpdv6hmaVhvWw@mail.gmail.com>

On Sat, Apr 28, 2018 at 10:01:57AM +0000, Timofey Titovets wrote:
> May be i misunderstood something, but i was think that slab combine
> several pages in continuous range, so object in slab can cross page
> boundary.  So, all calculation will be very depends on scale of slab
> size.
> 
> i.e. on my machine that looks quite different:
> name                    <active_objs>  <num_objs>  <objsize>  <objperslab>   <pagesperslab>
> btrfs_inode             142475         146272      1136       28             8
> 
> So,
> PAGE_SIZE * pagesperslab / objperslab
> 4096 * 8 / 28 = 1170.28
> 
> 4096*8 - 1136*28 = 960
> 
> That's looks like object can cross page boundary in slab.
> So, if size reduced to 1128,
> 4096 * 8 / 29 = 1129.93
> 4096*8 - 1128*29 = 56
> 
> Did i miss something?

Then this depends on the allocator, SLAB does 4k pages and SLUB 32k, so
there's a value in reducing the inode size.

      reply	other threads:[~2018-05-01 15:42 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-24 23:37 [PATCH 0/4] [RESEND] Btrfs: just bunch of patches to ioctl.c Timofey Titovets
2018-04-24 23:37 ` [PATCH 1/4] [RESEND] Btrfs: btrfs_dedupe_file_range() ioctl, remove 16MiB restriction Timofey Titovets
2018-04-26 14:03   ` David Sterba
2018-04-28  9:35     ` Timofey Titovets
2018-04-24 23:37 ` [PATCH 2/4] [RESEND] Btrfs: make should_defrag_range() understood compressed extents Timofey Titovets
2018-04-24 23:37 ` [PATCH 3/4] [RESEND] Btrfs: allow btrfs_defrag_file() uncompress files on defragmentation Timofey Titovets
2018-04-24 23:37 ` [PATCH 4/4] [RESEND] Btrfs: reduce size of struct btrfs_inode Timofey Titovets
2018-04-26 13:42   ` David Sterba
2018-04-28 10:01     ` Timofey Titovets
2018-05-01 15:39       ` David Sterba [this message]

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