Messages in this thread | | | Date | Tue, 20 Dec 2022 19:55:36 +0530 | From | Deepak R Varma <> | Subject | Re: kvzalloc vs kvcalloc |
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On Tue, Dec 20, 2022 at 08:13:19AM -0600, Gustavo A. R. Silva wrote: > > > On 12/20/22 01:48, Julia Lawall wrote: > > > > > > On Tue, 20 Dec 2022, Deepak R Varma wrote: > > > > > On Tue, Dec 20, 2022 at 08:39:09AM +0100, Julia Lawall wrote: > > > > > > > > > > > > On Tue, 20 Dec 2022, Deepak R Varma wrote: > > > > > > > > > On Tue, Dec 20, 2022 at 07:08:24AM +0100, Julia Lawall wrote: > > > > > > > > > > > > > > > > > > On Tue, 20 Dec 2022, Deepak R Varma wrote: > > > > > > > > > > > > > Hello Gustavo and Julia, > > > > > > > I was working on building a patch proposal using the kvmalloc.cocci file for a > > > > > > > driver. The recommendation from the semantic patch is to use kvzalloc instead of > > > > > > > a fallback memory allocation model. Please see my patch submitted here [1]. > > > > > > > > > > > > > > I also found another patch submitted by Gustavo [2] which suggests using > > > > > > > kvcalloc instead of kvzalloc. Unfortunately, I was not able to understand the > > > > > > > reasons/advantages using kvcalloc over kvzalloc. > > Look for the definitions of those functions and try to understand their differences. > In many cases you have go down the rabbit hole, but you should be able to get a good > grasp of the thing in question before hitting the bottom. :) > > Look for a couple of instances in the codebase where those functions are being used > and try to understand a bit of the context around them. In some cases reading the > commit logs is necessary.
Hello Gustavo, Thank you very much for the suggestion here. I will get deeper into the codebase and try to self learn. Your advise on reading the past commit logs is useful as well.
Thank you again!
./drv
> > > > > > > > > > > > > The calloc variants are for zeroed arrays. zalloc variants just zero. > > > > > > > > > > Thank you Julia and sorry to have missed the references in my email: > > > > > > > > In Gustavo's case, the array has a certain number of elements of a certain > > > > size. I don't know if you have both pieces of information in your case. > > > > calloc functions take them in separately, and do the multiplication in a > > > > way that checks for overflows. > > > > > > That is correct and I do have both the pieces, the size and number. This > > > actually further optimizes the code. We can eliminate the array_size variable > > > with the kvcalloc implementation. It is not used beyond the memory allocation. > > > > > > Please this code snip: > > > > > > 853 int count = size >> PAGE_SHIFT; > > > 1 int array_size = count * sizeof(struct page *); > > > 2 int i = 0; > > > 3 int order_idx = 0; > > > 4 > > > 5 pages = kvzalloc(array_size, GFP_KERNEL); > > > 6 if (!pages) > > > 7 return NULL; > > > > > > Thank you for your advise. I will wait to see Gustavo has any further guidance. > > > I will send in a revision to my patch accordingly. > > > > Great. A calloc function definitely looks like a good choice here. > > As Julia suggested, and as you may had realized already, the calloc function is the > way to go, in this case. > > -- > Gustavo > >
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