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From:   "Benjamin Coddington" <bcodding@redhat.com>
To:     trondmy@kernel.org
Cc:     linux-nfs@vger.kernel.org
Subject: Re: [PATCH 02/12] NFS: Clean up readdir struct nfs_cache_array
Date:   Tue, 03 Nov 2020 09:34:06 -0500
Message-ID: <37BCFCA0-58EE-499F-8A45-435C6C3925CA@redhat.com>
In-Reply-To: <ACB62869-286C-4189-9BF9-C4F622C02C73@redhat.com>
References: <20201102180658.6218-1-trondmy@kernel.org>
 <20201102180658.6218-2-trondmy@kernel.org>
 <20201102180658.6218-3-trondmy@kernel.org>
 <015FB69A-1E45-4A93-89F3-2755F2A565F0@redhat.com>
 <ACB62869-286C-4189-9BF9-C4F622C02C73@redhat.com>
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On 3 Nov 2020, at 9:09, Benjamin Coddington wrote:

> On 3 Nov 2020, at 8:35, Benjamin Coddington wrote:
>
>> On 2 Nov 2020, at 13:06, trondmy@kernel.org wrote:
>>
>>> From: Trond Myklebust <trond.myklebust@hammerspace.com>
>>>
>>> Since the 'eof_index' is only ever used as a flag, make it so.
>>> Also add a flag to detect if the page has been completely filled.
>>>
>>> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
>>> ---
>>>  fs/nfs/dir.c | 66 
>>> ++++++++++++++++++++++++++++++++++++++--------------
>>>  1 file changed, 49 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
>>> index 67d8595cd6e5..604ebe015387 100644
>>> --- a/fs/nfs/dir.c
>>> +++ b/fs/nfs/dir.c
>>> @@ -138,9 +138,10 @@ struct nfs_cache_array_entry {
>>>  };
>>>
>>>  struct nfs_cache_array {
>>> -	int size;
>>> -	int eof_index;
>>>  	u64 last_cookie;
>>> +	unsigned int size;
>>> +	unsigned char page_full : 1,
>>> +		      page_is_eof : 1;
>>>  	struct nfs_cache_array_entry array[];
>>>  };
>>>
>>> @@ -172,7 +173,6 @@ void nfs_readdir_init_array(struct page *page)
>>>
>>>  	array = kmap_atomic(page);
>>>  	memset(array, 0, sizeof(struct nfs_cache_array));
>>> -	array->eof_index = -1;
>>>  	kunmap_atomic(array);
>>>  }
>>>
>>> @@ -192,6 +192,17 @@ void nfs_readdir_clear_array(struct page *page)
>>>  	kunmap_atomic(array);
>>>  }
>>>
>>> +static void nfs_readdir_array_set_eof(struct nfs_cache_array 
>>> *array)
>>> +{
>>> +	array->page_is_eof = 1;
>>> +	array->page_full = 1;
>>> +}
>>> +
>>> +static bool nfs_readdir_array_is_full(struct nfs_cache_array 
>>> *array)
>>> +{
>>> +	return array->page_full;
>>> +}
>>> +
>>>  /*
>>>   * the caller is responsible for freeing qstr.name
>>>   * when called by nfs_readdir_add_to_array, the strings will be 
>>> freed in
>>> @@ -213,6 +224,23 @@ int nfs_readdir_make_qstr(struct qstr *string, 
>>> const char *name, unsigned int le
>>>  	return 0;
>>>  }
>>>
>>> +/*
>>> + * Check that the next array entry lies entirely within the page 
>>> bounds
>>> + */
>>> +static int nfs_readdir_array_can_expand(struct nfs_cache_array 
>>> *array)
>>> +{
>>> +	struct nfs_cache_array_entry *cache_entry;
>>> +
>>> +	if (array->page_full)
>>> +		return -ENOSPC;
>>> +	cache_entry = &array->array[array->size + 1];
>>> +	if ((char *)cache_entry - (char *)array > PAGE_SIZE) {
>>> +		array->page_full = 1;
>>> +		return -ENOSPC;
>>> +	}
>>> +	return 0;
>>> +}
>>> +
>>
>> I think we could do this calculation at compile-time instead of doing 
>> it for
>> each entry, for dubious nominal gains..
>
> and doing so might allow us to detect the case where the array is full
> before doing another RPC that we'll discard.

And you handle this case in patch 4/12...

Ben