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Sender: Ingo Molnar <mingo.kernel.org@gmail.com>
Date:   Wed, 7 Sep 2022 09:30:18 +0200
From:   Ingo Molnar <mingo@kernel.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     rjw@rjwysocki.net, oleg@redhat.com, vincent.guittot@linaro.org,
        dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de,
        ebiederm@xmission.com, bigeasy@linutronix.de,
        Will Deacon <will@kernel.org>, linux-kernel@vger.kernel.org,
        tj@kernel.org, linux-pm@vger.kernel.org
Subject: Re: [PATCH v3 6/6] freezer,sched: Rewrite core freezer logic
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* Peter Zijlstra <peterz@infradead.org> wrote:

> On Sun, Sep 04, 2022 at 12:09:37PM +0200, Ingo Molnar wrote:
> 
> > BTW., we should probably mark/document all PF_ holes with a PF__RESERVED 
> > kind of scheme? Something simple, like:
> > 
> >    #define PF_NPROC_EXCEEDED	0x00001000	/* set_user() noticed that RLIMIT_NPROC was exceeded */
> >    #define PF_USED_MATH		0x00002000	/* If unset the fpu must be initialized before use */
> >  + #define PF__RESERVED_04000	0x00004000	/* Unused */
> >    #define PF_NOFREEZE		0x00008000	/* This thread should not be frozen */
> >  + #define PF__RESERVED_10000	0x00010000	/* Unused */
> >    #define PF_KSWAPD		0x00020000	/* I am kswapd */
> >    #define PF_MEMALLOC_NOFS	0x00040000	/* All allocation requests will inherit GFP_NOFS */
> >    #define PF_MEMALLOC_NOIO	0x00080000	/* All allocation requests will inherit GFP_NOIO */
> 
> 
> How's this then, it immediately shows how holey it is :-)
> 
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1722,7 +1722,9 @@ extern struct pid *cad_pid;
>  #define PF_MEMALLOC		0x00000800	/* Allocating memory */
>  #define PF_NPROC_EXCEEDED	0x00001000	/* set_user() noticed that RLIMIT_NPROC was exceeded */
>  #define PF_USED_MATH		0x00002000	/* If unset the fpu must be initialized before use */
> +#define PF__HOLE__00004000	0x00004000	/* A HOLE */
>  #define PF_NOFREEZE		0x00008000	/* This thread should not be frozen */
> +#define PF__HOLE__00010000	0x00010000	/* A HOLE */
>  #define PF_KSWAPD		0x00020000	/* I am kswapd */
>  #define PF_MEMALLOC_NOFS	0x00040000	/* All allocation requests will inherit GFP_NOFS */
>  #define PF_MEMALLOC_NOIO	0x00080000	/* All allocation requests will inherit GFP_NOIO */
> @@ -1730,9 +1732,14 @@ extern struct pid *cad_pid;
>  						 * I am cleaning dirty pages from some other bdi. */
>  #define PF_KTHREAD		0x00200000	/* I am a kernel thread */
>  #define PF_RANDOMIZE		0x00400000	/* Randomize virtual address space */
> +#define PF__HOLE__00800000	0x00800000	/* A HOLE */
> +#define PF__HOLE__01000000	0x01000000	/* A HOLE */
> +#define PF__HOLE__02000000	0x02000000	/* A HOLE */
>  #define PF_NO_SETAFFINITY	0x04000000	/* Userland is not allowed to meddle with cpus_mask */
>  #define PF_MCE_EARLY		0x08000000      /* Early kill for mce process policy */
>  #define PF_MEMALLOC_PIN		0x10000000	/* Allocation context constrained to zones which allow long term pinning. */
> +#define PF__HOLE__20000000	0x20000000	/* A HOLE */
> +#define PF__HOLE__40000000	0x40000000	/* A HOLE */
>  #define PF_SUSPEND_TASK		0x80000000      /* This thread called freeze_processes() and should not be frozen */

LGTM - OTOH this looks quite a bit more cluttery than I imagined it in my 
head. :-/ So I'd leave out the comment part at minimum. With that:

Reviewed-by: Ingo Molnar <mingo@kernel.org>

Thanks,

	Ingo