On 02/12/18 00:58, Rasmus Villemoes wrote:
> On 2018-02-12 07:27, frowand.list@xxxxxxxxx wrote:
>> From: Frank Rowand <frank.rowand@xxxxxxxx>
>>
>> Create a cache of the nodes that contain a phandle property. Use this
>> cache to find the node for a given phandle value instead of scanning
>> the devicetree to find the node. If the phandle value is not found
>> in the cache, of_find_node_by_phandle() will fall back to the tree
>> scan algorithm.
>>
>> The cache is initialized in of_core_init().
>>
>> The cache is freed via a late_initcall_sync() if modules are not
>> enabled.
>
> Maybe a few words about the memory consumption of this solution versus
> the other proposed ones.
The patch comment is about this patch, not the other proposals.
Please do not take that as a snippy response. There were several
emails in the previous thread that discussed memory. In that
thread I responded as to how I would address the concerns. If
anyone wants to raise concerns about memory usage as a result of
this version of the patch they should do so in this current thread.
> Other nits below.
>
>> +static void of_populate_phandle_cache(void)
>> +{
>> + unsigned long flags;
>> + phandle max_phandle;
>> + u32 nodes = 0;
>> + struct device_node *np;
>> +
>> + if (phandle_cache)
>> + return;
>
> What's the point of that check?
Sanity check to make sure a memory leak of a previous cache
does not occur. I'll change it to free the cache if it
exists.
There is only one instance of of_populate_cache() being called,
so this is a theoretical issue. I intend to add another caller
in the devicetree overlay code in the future, but do not want
to do that now, to avoid a conflict with the overlay patch
series that has been in parallel development, and for which
I submitted v2 shortly after this set of patches.
> And shouldn't it be done inside the
> spinlock if at all?
Not an issue yet, but I'll keep my eye on the possibility of races
when I add a call to of_populate_cache() from the overlay code.
>> + max_phandle = live_tree_max_phandle();
>> +
>> + raw_spin_lock_irqsave(&devtree_lock, flags);
>> +
>> + for_each_of_allnodes(np)
>> + nodes++;
>
> Why not save a walk over all nodes and a spin_lock/unlock pair by
> combining the node count with the max_phandle computation? But you've
> just moved the existing live_tree_max_phandle, so probably better as a
> followup patch.
I'll consider adding the node counting into live_tree_max_phandle() later.
The other user of live_tree_max_phandle() is being modified in my overlay
patch series (see mention above). I don't want to create a conflict between
the two series.
>> + /* sanity cap for malformed tree */
>> + if (max_phandle > nodes)
>> + max_phandle = nodes;
>> +
>> + phandle_cache = kzalloc((max_phandle + 1) * sizeof(*phandle_cache),
>> + GFP_ATOMIC);
>
> Maybe kcalloc. Sure, you've capped max_phandle so there's no real risk
> of overflow.
OK, will do.
>> + for_each_of_allnodes(np)
>> + if (np->phandle != OF_PHANDLE_ILLEGAL &&
>> + np->phandle <= max_phandle &&
>> + np->phandle)
>
> I'd reverse the order of these conditions so that for all the nodes with
> no phandle we only do the np->phandle check. Also, extra whitespace
> before &&.
Will do.
>> + phandle_cache[np->phandle] = np;
>> +
>> + max_phandle_cache = max_phandle;
>> +
>> + raw_spin_unlock_irqrestore(&devtree_lock, flags);
>> +}
>> +
>
> Rasmus
>
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