linux-kernel - Re: [PATCH net-next v5 1/5] mm: add a signature in struct page

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Message-ID: <CAFnufp3pCrywDFXZqDSw+-2K7p9yHfYY9C5WveaXMWDJ_oViAA@mail.gmail.com>
Date:   Fri, 14 May 2021 03:34:02 +0200
From:   Matteo Croce <mcroce@...ux.microsoft.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     netdev@...r.kernel.org, linux-mm@...ck.org,
        Ayush Sawal <ayush.sawal@...lsio.com>,
        Vinay Kumar Yadav <vinay.yadav@...lsio.com>,
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        Sven Auhagen <sven.auhagen@...eatech.de>
Subject: Re: [PATCH net-next v5 1/5] mm: add a signature in struct page

On Fri, May 14, 2021 at 3:01 AM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Thu, May 13, 2021 at 06:58:42PM +0200, Matteo Croce wrote:
> >               struct {        /* page_pool used by netstack */
> > +                     /**
> > +                      * @pp_magic: magic value to avoid recycling non
> > +                      * page_pool allocated pages.
> > +                      * It aliases with page->lru.next
>
> I'm not really keen on documenting what aliases with what.
> pp_magic also aliases with compound_head, 'next' (for slab),
> and dev_pagemap.  This is an O(n^2) documentation problem ...
>

Eric asked to document what page->signature aliases, so I did it in
the commit message and in a comment.
I can drop the code comment and leave it just the commit message.

> I feel like I want to document the pfmemalloc bit in mm_types.h,
> but I don't have a concrete suggestion yet.
>
> > +++ b/include/net/page_pool.h
> > @@ -63,6 +63,8 @@
> >   */
> >  #define PP_ALLOC_CACHE_SIZE  128
> >  #define PP_ALLOC_CACHE_REFILL        64
> > +#define PP_SIGNATURE         (POISON_POINTER_DELTA + 0x40)
>
> I wonder if this wouldn't be better in linux/poison.h?
>

I was thinking the same, I'll do it in the v6.

Regards,
-- 
per aspera ad upstream