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From:   Joel Fernandes <joel@joelfernandes.org>
Date:   Tue, 30 Jul 2019 09:06:36 -0400
Message-ID: <CAEXW_YQN+htU-LpYQ_jxepVdRhO0byw1pWFrsbU2XsH=8FDKLA@mail.gmail.com>
Subject: Re: [PATCH v3 1/2] mm/page_idle: Add per-pid idle page tracking using
 virtual indexing
To:     LKML <linux-kernel@vger.kernel.org>
Cc:     Alexey Dobriyan <adobriyan@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Brendan Gregg <bgregg@netflix.com>,
        Christian Hansen <chansen3@cisco.com>,
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        Joel Fernandes <joelaf@google.com>,
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On Fri, Jul 26, 2019 at 11:23 AM Joel Fernandes (Google)
<joel@joelfernandes.org> wrote:
>
> The page_idle tracking feature currently requires looking up the pagemap
> for a process followed by interacting with /sys/kernel/mm/page_idle.
> Looking up PFN from pagemap in Android devices is not supported by
> unprivileged process and requires SYS_ADMIN and gives 0 for the PFN.
>
> This patch adds support to directly interact with page_idle tracking at
> the PID level by introducing a /proc/<pid>/page_idle file.  It follows
> the exact same semantics as the global /sys/kernel/mm/page_idle, but now
> looking up PFN through pagemap is not needed since the interface uses
> virtual frame numbers, and at the same time also does not require
> SYS_ADMIN.
>
> In Android, we are using this for the heap profiler (heapprofd) which
> profiles and pin points code paths which allocates and leaves memory
> idle for long periods of time. This method solves the security issue
> with userspace learning the PFN, and while at it is also shown to yield
> better results than the pagemap lookup, the theory being that the window
> where the address space can change is reduced by eliminating the
> intermediate pagemap look up stage. In virtual address indexing, the
> process's mmap_sem is held for the duration of the access.
>
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
>
> ---
> v2->v3:
> Fixed a bug where I was doing a kfree that is not needed due to not
> needing to do GFP_ATOMIC allocations.
>
> v1->v2:
> Mark swap ptes as idle (Minchan)
> Avoid need for GFP_ATOMIC (Andrew)
> Get rid of idle_page_list lock by moving list to stack

I believe all suggestions have been addressed.  Do these look good now?

thanks,

 - Joel


> Internal review -> v1:
> Fixes from Suren.
> Corrections to change log, docs (Florian, Sandeep)
>
>  fs/proc/base.c            |   3 +
>  fs/proc/internal.h        |   1 +
>  fs/proc/task_mmu.c        |  57 +++++++
>  include/linux/page_idle.h |   4 +
>  mm/page_idle.c            | 340 +++++++++++++++++++++++++++++++++-----
>  5 files changed, 360 insertions(+), 45 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 77eb628ecc7f..a58dd74606e9 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -3021,6 +3021,9 @@ static const struct pid_entry tgid_base_stuff[] = {
>         REG("smaps",      S_IRUGO, proc_pid_smaps_operations),
>         REG("smaps_rollup", S_IRUGO, proc_pid_smaps_rollup_operations),