linux-kernel - Re: [PATCH 5/6] treewide: use kv[mz]alloc* rather than opencoded variants

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Date:   Sat, 14 Jan 2017 12:01:50 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] treewide: use kv[mz]alloc* rather than opencoded
 variants

On 2017/01/13 2:29, Michal Hocko wrote:
> Ilya has noticed that I've screwed up some k[zc]alloc conversions and
> didn't use the kvzalloc. This is an updated patch with some acks
> collected on the way
> ---
> From a7b89c6d0a3c685045e37740c8f97b065f37e0a4 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@...e.com>
> Date: Wed, 4 Jan 2017 13:30:32 +0100
> Subject: [PATCH] treewide: use kv[mz]alloc* rather than opencoded variants
> 
> There are many code paths opencoding kvmalloc. Let's use the helper
> instead. The main difference to kvmalloc is that those users are usually
> not considering all the aspects of the memory allocator. E.g. allocation
> requests < 64kB are basically never failing and invoke OOM killer to

Isn't this "requests <= 32kB" because allocation requests for 33kB will be
rounded up to 64kB?

Same for "smaller than 64kB" in PATCH 6/6. But strictly speaking, isn't
it bogus to refer actual size because PAGE_SIZE is not always 4096?

---------- arch/ia64/include/asm/page.h ----------
/*
 * PAGE_SHIFT determines the actual kernel page size.
 */
#if defined(CONFIG_IA64_PAGE_SIZE_4KB)
# define PAGE_SHIFT     12
#elif defined(CONFIG_IA64_PAGE_SIZE_8KB)
# define PAGE_SHIFT     13
#elif defined(CONFIG_IA64_PAGE_SIZE_16KB)
# define PAGE_SHIFT     14
#elif defined(CONFIG_IA64_PAGE_SIZE_64KB)
# define PAGE_SHIFT     16
#else
# error Unsupported page size!
#endif

#define PAGE_SIZE               (__IA64_UL_CONST(1) << PAGE_SHIFT)


> satisfy the allocation. This sounds too disruptive for something that
> has a reasonable fallback - the vmalloc. On the other hand those
> requests might fallback to vmalloc even when the memory allocator would
> succeed after several more reclaim/compaction attempts previously. There
> is no guarantee something like that happens though.
> 
> This patch converts many of those places to kv[mz]alloc* helpers because
> they are more conservative.