linux-kernel - Re: [PATCH v2 7/7] docs/core-api: mm-api: add section about GFP flags

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Message-ID: <20180726142039.GA23627@dhcp22.suse.cz>
Date:   Thu, 26 Jul 2018 16:20:39 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 7/7] docs/core-api: mm-api: add section about GFP flags

On Thu 26-07-18 06:01:06, Matthew Wilcox wrote:
> On Thu, Jul 26, 2018 at 03:22:02PM +0300, Mike Rapoport wrote:
> > +Memory Allocation Controls
> > +==========================
> 
> Perhaps call this section "Memory Allocation Flags" instead?
> 
> > +Linux provides a variety of APIs for memory allocation from direct
> > +calls to page allocator through slab caches and vmalloc to allocators
> > +of compressed memory. Although these allocators have different
> > +semantics and are used in different circumstances, they all share the
> > +GFP (get free page) flags that control behavior of each allocation
> > +request.
> 
> While this isn't /wrong/, I think it might not be the most useful way
> of explaining what the GFP flags are to someone who's just come across
> them in some remote part of the kernel.  How about this paragraph instead?
> 
>   Functions which need to allocate memory often use GFP flags to express
>   how that memory should be allocated.  The GFP acronym stands for "get
>   free pages", the underlying memory allocation function.

OK.

>   Not every GFP
>   flag is allowed to every function which may allocate memory.  Most
>   users will want to use a plain ``GFP_KERNEL`` or ``GFP_ATOMIC``.

Or rather than mentioning the two just use "Useful GFP flag
combinations" comment segment from gfp.h
-- 
Michal Hocko
SUSE Labs