On 24 Feb 2022, at 21:11, Trond Myklebust wrote:
> On Thu, 2022-02-24 at 09:15 -0500, Benjamin Coddington wrote:
>> On 23 Feb 2022, at 16:12, trondmy@xxxxxxxxxx wrote:
>>
>>> From: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
>>>
>>> Instead of relying on counting the page offsets as we walk through
>>> the
>>> page cache, switch to calculating them algorithmically.
>>>
>>> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
>>> ---
>>> fs/nfs/dir.c | 18 +++++++++++++-----
>>> 1 file changed, 13 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
>>> index 8f17aaebcd77..f2258e926df2 100644
>>> --- a/fs/nfs/dir.c
>>> +++ b/fs/nfs/dir.c
>>> @@ -248,17 +248,20 @@ static const char
>>> *nfs_readdir_copy_name(const
>>> char *name, unsigned int len)
>>> return ret;
>>> }
>>>
>>> +static size_t nfs_readdir_array_maxentries(void)
>>> +{
>>> + return (PAGE_SIZE - sizeof(struct nfs_cache_array)) /
>>> + sizeof(struct nfs_cache_array_entry);
>>> +}
>>> +
>>
>> Why the choice to use a runtime function call rather than the
>> compiler's
>> calculation? I suspect that the end result is the same, as the
>> compiler
>> will optimize it away, but I'm curious if there's a good reason for
>> this.
>>
>
> The comparison is more efficient because no pointer arithmetic is
> needed. As you said, the above function always evaluates to a constant,
> and the array->size has been pre-calculated.
Comparisons are more efficient than using something like this?:
static const int nfs_readdir_array_maxentries =
(PAGE_SIZE - sizeof(struct nfs_cache_array)) /
sizeof(struct nfs_cache_array_entry);
I don't understand why, I must admit. I'm not saying it should be changed,
I'm just trying to figure out the reason for the function declaration when
the value is a constant, and I thought there was a hole in my head.
Ben
