Re: [PATCH 2/2] blk-iocost: Use alloc_percpu_gfp() to simplify the code

From: Baolin Wang
Date: Fri Dec 11 2020 - 02:15:04 EST


Hi Tejun,

Hello,

On Thu, Dec 10, 2020 at 06:56:45PM +0800, Baolin Wang wrote:
Use alloc_percpu_gfp() with __GFP_ZERO flag, which can remove
some explicit initialization code.

__GFP_ZERO is implicit for percpu allocations and local[64]_t's initial
states aren't guaranteed to be all zeros on different archs.

Thanks for teaching me this, at least I did not get this from the local_ops Documentation before. Just out of curiosity, these local[64]_t variables are also allocated from budy allocator ultimately, why they can not be initialized to zeros on some ARCHs with __GFP_ZERO? Could you elaborate on about this restriction? Thanks.

By the way, seems the kyber-iosched has the same issue, since the 'struct kyber_cpu_latency' also contains an atomic_t variable.

kqd->cpu_latency = alloc_percpu_gfp(struct kyber_cpu_latency,
GFP_KERNEL | __GFP_ZERO);
if (!kqd->cpu_latency)
goto err_kqd;