Re: [pbs-devel] [PATCH proxmox-backup 0/5] GC: avoid multiple atime updates

From: Christian Ebner <c.ebner@proxmox.com>
To: Roland <devzero@web.de>,
	Proxmox Backup Server development discussion
	<pbs-devel@lists.proxmox.com>
Subject: Re: [pbs-devel] [PATCH proxmox-backup 0/5] GC: avoid multiple atime updates
Date: Fri, 21 Feb 2025 16:49:33 +0100	[thread overview]
Message-ID: <61d2c6aa-7143-4415-82b3-ee2b4220fa5d@proxmox.com> (raw)
In-Reply-To: <dd4f458f-e64b-4061-a94f-4cd565f1f385@web.de>

On 2/21/25 16:35, Roland wrote:
> hello,
> 
> this looks like this relates to or adresses what's being mentioned here ?
> 
> https://forum.proxmox.com/threads/better-understand-proxmox-garbage- 
> collection-lots-of-avoidable-utimensat-calls.101417/
> ?
> 
> it came to my mind when reading this.  not sure if i did an RFE for
> this, guess i forgot...

Yes, this has been requested also by others, see the discussion in 
https://bugzilla.proxmox.com/show_bug.cgi?id=5331

The (still initial) title of the issue is a bit misleading, as the 
implementation in the patch series works for all chunks, not just the 
zero chunks. ;)

> 
>  >for my curiosity, i see there is one chunk in both of my homeserver
> repos which is accessed orders of magnitudes more often then all
>  >the other chunks (for one repo roundabout 1000x more often) during gc
> run. anyhow, many chunks are being acessed repeatedly, but at a much
> lower rate.
> 
> ah, now i understand why that file is touched 34742 times - it's that
> "all zeroes" chunk, which does occur in the vm image much more often.

Haven't check that yet, but most likely yes, I do have the same chunk in 
my datastore.

> 
> 34742 proxmox-backup-(1428): R
> /backup/pve-t620_backup/.chunks/bb9f/ 
> bb9f8df61474d25e71fa00722318cd387396ca1736605e1248821cc0de3d3af8
> 
> any clue what's this one,  which is being touched an order of magnitude
> more often then the zeroes chunk ?

I do not have that particular chunk digest in my datastores, but if the 
chunk is not encrypted, you could just decompress it and inspect the 
contents via a hex editor.

> 
> 940079 proxmox-backup-(1428): R
> /backup/pve-maker- 
> bonn_backup/.chunks/7b27/7b27b1eb4febae3273321255d8304e9b3e7938d9e254564bef859a4307a88638
> 
> regards
> roland

Cheers,
Chris

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