linux-kernel - Re: [PATCH v2] s390/zcrypt: optimizes memory allocation in online

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Date: Wed, 26 Jun 2024 16:55:57 +0900
From: Yunseong Kim <yskelg@...il.com>
To: freude@...ux.ibm.com
Cc: Markus Elfring <Markus.Elfring@....de>, Heiko Carstens
 <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, MichelleJin <shjy180909@...il.com>,
 linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
 Holger Dengler <dengler@...ux.ibm.com>
Subject: Re: [PATCH v2] s390/zcrypt: optimizes memory allocation in
 online_show()

Hi Harald,

On 6/25/24 5:27 오후, Harald Freudenberger wrote:
> On 2024-06-25 00:29, yskelg@...il.com wrote:
>> From: Yunseong Kim <yskelg@...il.com>
>>
>> Make memory allocation more precise (based on maxzqs) by allocating
>> memory only for the queues that are truly affected by the online state
>> changes.
>>
>> Fixes: df6f508c68db ("s390/ap/zcrypt: notify userspace with online,
>> config and mode info")
>> Link:
>> https://lore.kernel.org/linux-s390/your-ad-here.call-01625406648-ext-2488@work.hours/
> 
> What is this Link here? It is pointing to a PR for a 5.14 kernel and has
> no relation to this patch.
> 
>> Cc: linux-s390@...r.kernel.org
>> Signed-off-by: Yunseong Kim <yskelg@...il.com>
>> ---
>>  drivers/s390/crypto/zcrypt_card.c | 16 +++++++---------
>>  1 file changed, 7 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/s390/crypto/zcrypt_card.c
>> b/drivers/s390/crypto/zcrypt_card.c
>> index 050462d95222..2c80be3f2a00 100644
>> --- a/drivers/s390/crypto/zcrypt_card.c
>> +++ b/drivers/s390/crypto/zcrypt_card.c
>> @@ -88,9 +88,10 @@ static ssize_t online_store(struct device *dev,
>>       * the zqueue objects, we make sure they exist after lock release.
>>       */
>>      list_for_each_entry(zq, &zc->zqueues, list)
>> -        maxzqs++;
>> +        if (!!zq->online != !!online)
> 
> I don't like this line. It is code duplication from the zcrypt_queue.c file
> and uses knowledge about the internals of the zqueue which is not
> appropriate
> here in zcrypt_card.c. Please note also that usually the total number of
> queues attached to a card is in a one digit range. As kcalloc() anyway uses
> the kmalloc pool which is ordered in powers of two it is unlikely to really
> spare some memory by only allocating a pointer space for the online queues.

Thank you Harald for the code review! Oh I see, thanks for the advice.
I was wondering if it was useful when I was coding it too.

>> +            maxzqs++;
>>      if (maxzqs > 0)
>> -        zq_uelist = kcalloc(maxzqs + 1, sizeof(*zq_uelist), GFP_ATOMIC);
>> +        zq_uelist = kcalloc(maxzqs, sizeof(*zq_uelist), GFP_ATOMIC);
> 
> Your improvement about removal of the +1 and use the i value later instead
> of my implementation which uses a NULL as end of list is valid and makes
> sense
> to me.
> 
>>      list_for_each_entry(zq, &zc->zqueues, list)
>>          if (zcrypt_queue_force_online(zq, online))
>>              if (zq_uelist) {
>> @@ -98,14 +99,11 @@ static ssize_t online_store(struct device *dev,
>>                  zq_uelist[i++] = zq;
>>              }
>>      spin_unlock(&zcrypt_list_lock);
>> -    if (zq_uelist) {
>> -        for (i = 0; zq_uelist[i]; i++) {
>> -            zq = zq_uelist[i];
>> -            ap_send_online_uevent(&zq->queue->ap_dev, online);
>> -            zcrypt_queue_put(zq);
>> -        }
>> -        kfree(zq_uelist);
>> +    while (i--) {
>> +        ap_send_online_uevent(&zq->queue->ap_dev, online);
>> +        zcrypt_queue_put(zq_uelist[i]);
> 
> The content of this while loop is NOT covering the old code. zq is not
> set any more and thus the ap_sen_online_uevent() uses a random zq which
> is a left over from the list_for_each() loop.

Oh this is where I wrote the code without understanding it properly,
thanks for the guidance!

>>      }
>> +    kfree(zq_uelist);
>>
>>      return count;
>>  }
> 
> You sent another patch for the online_store() function with exactly the
> same code changes. I would see these changes as one patch and don't want
> to have more or less equal changes spread over two patches.
> 
> I am sorry, I will not pick this and the online_store() patch.

I'm so sorry Harald, This was missing judgment, I should have checked it
one last time before sending v2 patch mail.

> regards Harald Freudenberger


I truly appreciate Harald for the detailed code review of my patch.,
even though it may be less understanding in many part.

Thank you very much again!


Warm regards,

Yunseong Kim