Re: [PATCH] scatterlist: Allocate a contiguous array instead of chaining

[Ming Lei]

On Thu, Jul 11, 2019 at 11:36:56PM -0700, Sultan Alsawaf wrote:
> From: Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx>
> 
> Typically, drivers allocate sg lists of sizes up to a few MiB in size.
> The current algorithm deals with large sg lists by splitting them into
> several smaller arrays and chaining them together. But if the sg list
> allocation is large, and we know the size ahead of time, sg chaining is
> both inefficient and unnecessary.
> 
> Rather than calling kmalloc hundreds of times in a loop for chaining
> tiny arrays, we can simply do it all at once with kvmalloc, which has
> the proper tradeoff on when to stop using kmalloc and instead use
> vmalloc.

vmalloc() may sleep, so it is impossible to be called in atomic context.

Thanks,
Ming