linux-kernel - Re: [PATCH v3 1/1] swiotlb: Track and report io_tlb

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Date:   Tue, 11 Apr 2023 05:41:37 +0200
From:   "hch@....de" <hch@....de>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Cc:     Petr Tesařík <petr@...arici.cz>,
        "hch@....de" <hch@....de>,
        "m.szyprowski@...sung.com" <m.szyprowski@...sung.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        Dexuan Cui <decui@...rosoft.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/1] swiotlb: Track and report io_tlb_used high
 water mark in debugfs

On Fri, Apr 07, 2023 at 10:05:26PM +0000, Michael Kelley (LINUX) wrote:
> > Yes, this works fine now, but why are total_used and used_hiwater
> > global variables? If you make them fields in struct io_tlb_mem
> > (possibly guarded with #ifdef CONFIG_DEBUG_FS), you can get rid of the
> > check. Of course, in instances other than io_tlb_default_mem these
> > fields would not be exported to userspace through debugfs, but if really
> > needed, I can at least find them in a crash dump (or read them through
> > /proc/kcore).
> > 
> 
> Got it.
> 
> Your previously comments mentioned making them fields in struct io_tlb_mem,
> and I missed your point.  :-(   I got focused on fixing the accounting for
> DEBUG_FS so it didn't include the non-default pools, and didn't pick up on the
> idea of doing the accounting for the non-default pools even though the values
> aren't exposed in /sys.   I'll fix this in the next version.

FYI, I agree that per-instance accounting is probably the better way,
too.