linux-kernel - Re: [PATCH, RESEND] introduce get_mm_hiwater_xxx(), fix taskstats->hiwater

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Date:	Sat, 13 Dec 2008 11:34:53 +0900
From:	"KOSAKI Motohiro" <kosaki.motohiro@...fujitsu.com>
To:	"Oleg Nesterov" <oleg@...hat.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Balbir Singh" <balbir@...ux.vnet.ibm.com>,
	"Hugh Dickins" <hugh@...itas.com>, "Jay Lan" <jlan@....com>,
	"Jiri Pirko" <jpirko@...hat.com>, "Jonathan Lim" <jlim@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH, RESEND] introduce get_mm_hiwater_xxx(), fix taskstats->hiwater_xxx accounting

> (changes: update the changelog/comments)
>
> xacct_add_tsk() relies on do_exit()->update_hiwater_xxx() and uses
> mm->hiwater_xxx directly, this leads to 2 problems:
>
>        - taskstats_user_cmd() can call fill_pid()->xacct_add_tsk()
>          at any moment before the task exits, so we should check the
>          current values of rss/vm anyway.
>
>        - do_exit()->update_hiwater_xxx() calls are racy. An exiting
>          thread can be preempted right before mm->hiwater_xxx = new_val,
>          and another thread can use A_LOT of memory and exit in between.
>          When the first thread resumes it can be the last thread in the
>          thread group, in that case we report the wrong hiwater_xxx
>          values which do not take A_LOT into account.
>
> Introduce get_mm_hiwater_rss() and get_mm_hiwater_vm() helpers and
> change xacct_add_tsk() to use them. The first helper will also be
> used by rusage->ru_maxrss accounting.
>
> Kill do_exit()->update_hiwater_xxx() calls. Unless we are going to
> decrease rss/vm there is no point to update mm->hiwater_xxx, and
> nobody can look at this mm_struct when exit_mmap() actually unmaps
> the memory.
>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>

Thanks! looks good to me.
   Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>



> --- K-28/mm/mmap.c~HIWATER      2008-12-02 17:12:40.000000000 +0100
> +++ K-28/mm/mmap.c      2008-12-11 09:13:07.000000000 +0100
> @@ -2103,7 +2103,7 @@ void exit_mmap(struct mm_struct *mm)
>        lru_add_drain();
>        flush_cache_mm(mm);
>        tlb = tlb_gather_mmu(mm, 1);
> -       /* Don't update_hiwater_rss(mm) here, do_exit already did */
> +       /* update_hiwater_rss(mm) here? but nobody should be looking */
>        /* Use -1 here to ensure all VMAs in the mm are unmapped */
>        end = unmap_vmas(&tlb, vma, 0, -1, &nr_accounted, NULL);
>        vm_unacct_memory(nr_accounted);

I also think hiwatermark don't need update here.
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