Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH V7 20/24] bcache: avoid to use bio_for_each_segment_all()
 in bch_bio_alloc_pages()
To:     Ming Lei <ming.lei@redhat.com>
Cc:     Jens Axboe <axboe@fb.com>, Christoph Hellwig <hch@infradead.org>,
        Kent Overstreet <kent.overstreet@gmail.com>,
        David Sterba <dsterba@suse.cz>,
        Huang Ying <ying.huang@intel.com>,
        Mike Snitzer <snitzer@redhat.com>,
        linux-kernel@vger.kernel.org, linux-block@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        Theodore Ts'o <tytso@mit.edu>,
        "Darrick J . Wong" <darrick.wong@oracle.com>,
        Filipe Manana <fdmanana@gmail.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        linux-bcache@vger.kernel.org
References: <20180627124548.3456-1-ming.lei@redhat.com>
 <20180627124548.3456-21-ming.lei@redhat.com>
 <e1499d87-62b8-40a8-75a5-d9d1d81ce9c5@suse.de>
 <20180628012816.GH7583@ming.t460p>
From:   Coly Li <colyli@suse.de>
Openpgp: preference=signencrypt
Autocrypt: addr=colyli@suse.de; prefer-encrypt=mutual; keydata=
 xsFNBFYX6S8BEAC9VSamb2aiMTQREFXK4K/W7nGnAinca7MRuFUD4JqWMJ9FakNRd/E0v30F
 qvZ2YWpidPjaIxHwu3u9tmLKqS+2vnP0k7PRHXBYbtZEMpy3kCzseNfdrNqwJ54A430BHf2S
 GMVRVENiScsnh4SnaYjFVvB8SrlhTsgVEXEBBma5Ktgq9YSoy5miatWmZvHLFTQgFMabCz/P
 j5/xzykrF6yHo0rHZtwzQzF8rriOplAFCECp/t05+OeHHxjSqSI0P/G79Ll+AJYLRRm9til/
 K6yz/1hX5xMToIkYrshDJDrUc8DjEpISQQPhG19PzaUf3vFpmnSVYprcWfJWsa2wZyyjRFkf
 J51S82WfclafNC6N7eRXedpRpG6udUAYOA1YdtlyQRZa84EJvMzW96iSL1Gf+ZGtRuM3k49H
 1wiWOjlANiJYSIWyzJjxAd/7Xtiy/s3PRKL9u9y25ftMLFa1IljiDG+mdY7LyAGfvdtIkanr
 iBpX4gWXd7lNQFLDJMfShfu+CTMCdRzCAQ9hIHPmBeZDJxKq721CyBiGAhRxDN+TYiaG/UWT
 7IB7LL4zJrIe/xQ8HhRO+2NvT89o0LxEFKBGg39yjTMIrjbl2ZxY488+56UV4FclubrG+t16
 r2KrandM7P5RjR+cuHhkKseim50Qsw0B+Eu33Hjry7YCihmGswARAQABzRhDb2x5IExpIDxj
 b2x5bGlAc3VzZS5kZT7CwX8EEwEIACkFAlYX6ZACGyMFCQlmAYAHCwkIBwMCAQYVCAIJCgsE
 FgIDAQIeAQIXgAAKCRDHOQeTa334/CncD/9B97EIjcDOm0TS164bpMlsbZWEm8GQnV6nVzm8
 QsywPRM8S8nqkqX1atTYl/fTdJsasH8mgryUqL0eHBPs5RmJhDk3YgYsTrzbOjMdsdRwv24W
 J5RXdulRag2XDPIhSP7rWsOSh66gljdAp8XQQZD0zFXi4IytoAuLtx8RMjzzKk1iP6uz8MIv
 em7iFu6NYcHd3cmvSPo7CnBVaG0dZ6P2p2gS7ydSWOGsWkNh/XM4ojJaX1ZdCeFR0XLS76Gi
 6e01DoN2UsqZE/TQu1czYMMA1uM/Es6ZTYgobTrrnNB79ctqgtbBrjME5sOHLX40ccbBI3QB
 Ta4opSp8VqUMXw/yd5ckLPocnkJBTVxuaOfRhpxr6gWeudrkMetMj+39yeklskP7up0JvAUG
 7/HjjqwWR7xAaZHmZORYsIxJ9ploBb8eSqHHx+7489ZDNLP+WCsAonpKTdJNAzGJClnLFxKS
 DY4cOPs7o4IFBk6dVXJWMqyLGwmMQ51Pq6BID4epaAuuBAL6x7n7NrFPuS68Fn/VaxqMEld9
 L2eCi4cv++1AJyMF3iQKT56I8BjHEuf0wo1tmZ3BgBT19xRsEl7YItixxtYQm66Pb4lSQQmE
 Ep+uQNwaqPpeAU+vkDg/0Q+dhPTsvwx0OAI30HwhuzNA8OIfHBx7dJNm0b0fg5x0pg3LDM7B
 TQRWF+kvARAA2T/tnJeA0RWkmgZrNPFvP7JnOU9gjmIQKMoGZ+9awew45pdmXb6y0Y0fEG59
 EP9i9oBlFXOt6SZ2645V0sdi3wBRNEpX2CCddWhXRfcO0b6lgckIwyaK92dH1rzxMaZTYDL8
 aQ9FNEK1U+XSBk8fYWnXowpf7oNPS6+jD0J/muPqrGkVsIAkh2iLg5B98yNTCV4ql1xSlMyf
 xcseke9q6ojDxx9p38JjLusDlwF2+/rF42c+T6PRiYNjnBHPq6VLSlCRsnkLJwg8VHKiV2Qw
 Yvxp4TwnK2kLqokOxBlriX45Odb2iP61uG2ZAPchDwfawWJ4G8+3EMplLH8bk0/DkpYcYz95
 eGSGRSiIQ2kHmTI/KbpgXxFVMoheilUn4HzUP+T6TEeP6Zhm0aqwABJYa0T2ykJwpBlg6/Mx
 vgIzdSheqx2hYACDu07WfhdvI6uK3i5Lq9DebUBcMMBcMc0TnXix7mYy+3hLXJzZ80pFx3My
 5FeJEN/r6/+xpuuZkH51aYOiacKVa2w2EHjhZcWfPhhEWOQ2oOCoCmv+HEmV9sf+fipEMfcB
 8GnJMOYAwrwHWfkPNZ5urUcRGAQYlQ0GWKju97LYE2cq5McpFG0CMvDyPoO1zAwjJz4g53EK
 oH/eikd3L8OMDfEK4AOsUaPMTnNgt1+40zEFMrQs/dDMldUAEQEAAcLBZQQYAQgADwUCVhfp
 LwIbDAUJCWYBgAAKCRDHOQeTa334/PtREACDN8W/pHeHyPW/mTt6MEe/GICG5YdlBW5ft7HY
 Cf6rTz+uLZolGc5SYKuJJ0JC/L2Ifh3BWmwLIOxV868KB3oEfmGszBY+4n/icLyIEAkkthBb
 2V5sP5KgB3bOg7mSFBxfHi2pyO9K9d+Lr+UkORjCGyV33QFrcN+OQdPDactontnQglB7xm2K
 phGWqxoqepHCqFIulZ3yKGhQhmdpyz0J19Ry6GkxPE85MG/NC98D5+4Yn/V3G+yZpbGsuFhE
 CP26JvdXh1jNCUdU46pEjZwu0GXBIo6r1cb1v+swfYB86NeFUHWtvxamh8i6RBl1FLDhN6xb
 r9f7M++xoADyzPQYQPQUxWK+iG6lz3qVVq5312z/is3fcdyESPNs09DMT43xCCBr9UOMq6dZ
 IC9EsSeMYv4librfuSRqH4R0MuVbVWLJFg/Q7s+nbPb2YjhqIYr51hBDyXpzUDoIz43maIPk
 UmCNKa43mNFktMrwU21J5lVXEwBuTY6JlHOAl0Fgo28X+eTa8fx2Uiz9OVgWe03ebJGIGowe
 XTgqVWJMsKM1tmW+QFmgtczDGRYCZ6OQYpqt0SoTg1yx5MN4RzUtlLka2qLfPiOGUUN3qNJ5
 nP+spvF+s+dHtLjjhy7AL86N01a6S0rwaClVVv0XTucvIntwccIx0CZfUKlfn5BWnB64Ig==
Message-ID: <92ae1547-39b1-472c-efbe-c0a6430fc3f6@suse.de>
Date:   Thu, 28 Jun 2018 10:01:39 +0800
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:52.0)
 Gecko/20100101 Thunderbird/52.8.0
MIME-Version: 1.0
In-Reply-To: <20180628012816.GH7583@ming.t460p>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 2018/6/28 9:28 AM, Ming Lei wrote:
> On Wed, Jun 27, 2018 at 11:55:33PM +0800, Coly Li wrote:
>> On 2018/6/27 8:45 PM, Ming Lei wrote:
>>> bch_bio_alloc_pages() is always called on one new bio, so it is safe
>>> to access the bvec table directly. Given it is the only kind of this
>>> case, open code the bvec table access since bio_for_each_segment_all()
>>> will be changed to support for iterating over multipage bvec.
>>>
>>> Cc: Coly Li <colyli@suse.de>
>>> Cc: linux-bcache@vger.kernel.org
>>> Signed-off-by: Ming Lei <ming.lei@redhat.com>
>>> ---
>>>  drivers/md/bcache/util.c | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/md/bcache/util.c b/drivers/md/bcache/util.c
>>> index fc479b026d6d..9f2a6fd5dfc9 100644
>>> --- a/drivers/md/bcache/util.c
>>> +++ b/drivers/md/bcache/util.c
>>> @@ -268,7 +268,7 @@ int bch_bio_alloc_pages(struct bio *bio, gfp_t gfp_mask)
>>>  	int i;
>>>  	struct bio_vec *bv;
>>>
>>
>> Hi Ming,
>>
>>> -	bio_for_each_segment_all(bv, bio, i) {
>>> +	for (i = 0, bv = bio->bi_io_vec; i < bio->bi_vcnt; bv++) {
>>
>>
>> Is it possible to treat this as a special condition of
>> bio_for_each_segement_all() ? I mean only iterate one time in
>> bvec_for_each_segment(). I hope the above change is not our last choice
>> before I reply an Acked-by :-)
> 
> Now the bvec from bio_for_each_segement_all() can't be changed any more
> since the referenced 'bvec' is generated in-flight given we store
> real multipage bvec.
> 
> BTW, this way is actually suggested by Christoph for saving one new
> helper of bio_for_each_bvec_all() as done in V6, and per previous discussion,
> seems both Kent and Christoph agrees to convert bcache into bio_add_page()
> finally.
> 
> So I guess this open code style should be fine.

Hi Ming,

I see, thanks for the hint.

Acked-by: Coly Li <colyli@suse.de>

Coly Li