linux-kernel - Re: [PATCH 0/6] second round of tracepoints for DAX

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Message-ID: <20170222105156.GC23312@quack2.suse.cz>
Date:   Wed, 22 Feb 2017 11:51:56 +0100
From:   Jan Kara <jack@...e.cz>
To:     Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Dan Williams <dan.j.williams@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-fsdevel@...r.kernel.org, linux-nvdimm@...ts.01.org
Subject: Re: [PATCH 0/6] second round of tracepoints for DAX

On Tue 21-02-17 12:51:10, Ross Zwisler wrote:
> This second round of DAX tracepoint patches adds tracing to the PTE fault
> path (dax_iomap_pte_fault(), dax_pfn_mkwrite(), dax_load_hole(),
> dax_insert_mapping()) and to the writeback path
> (dax_writeback_mapping_range(), dax_writeback_one()).
> 
> The purpose of this tracing is to give us a high level view of what DAX is
> doing, whether faults are being serviced by PMDs or PTEs, and by real
> storage or by zero pages covering holes.
> 
> I do have some patches nearly ready which also add tracing to
> grab_mapping_entry() and dax_insert_mapping_entry().  These are more
> targeted at logging how we are interacting with the radix tree, how we use
> empty entries for locking, whether we "downgrade" huge zero pages to
> 4k PTE sized allocations, etc.  In the end it seemed to me that this might
> be too detailed to have as constantly present tracepoints, but if anyone
> sees value in having tracepoints like this in the DAX code permanently
> (Jan?), please let me know and I'll add those last two patches.

Yeah, for now I think it is too detailed and high-level logging is good
enough. As we will debug problems, we may find places that are useful for
more detailed tracepoints but for now what you added looks fine.

> All these tracepoints were done to be consistent with the style of the XFS
> tracepoints and with the existing DAX PMD tracepoints.
> 
> This series applies cleanly to the current mmots/master:
> 
> commit 35aa45ffe8d9 ("pci: test for unexpectedly disabled bridges")
> 
> and I'm hoping that it'll end up going to Linus through akpm's -mm tree.

I like the patches and they look fine to me. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR