All of lore.kernel.org
 help / color / mirror / Atom feed
From: Michal Hocko <mhocko@kernel.org>
To: Vinayak Menon <vinmenon@codeaurora.org>
Cc: akpm@linux-foundation.org, hannes@cmpxchg.org,
	mgorman@techsingularity.net, vbabka@suse.cz, riel@redhat.com,
	vdavydov.dev@gmail.com, anton.vorontsov@linaro.org,
	minchan@kernel.org, shashim@codeaurora.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2 v2] mm: vmpressure: fix sending wrong events on underflow
Date: Thu, 9 Feb 2017 13:10:57 +0100	[thread overview]
Message-ID: <20170209121057.GF10257@dhcp22.suse.cz> (raw)
In-Reply-To: <1486641577-11685-1-git-send-email-vinmenon@codeaurora.org>

On Thu 09-02-17 17:29:36, Vinayak Menon wrote:
> At the end of a window period, if the reclaimed pages
> is greater than scanned, an unsigned underflow can
> result in a huge pressure value and thus a critical event.
> Reclaimed pages is found to go higher than scanned because
> of the addition of reclaimed slab pages to reclaimed in
> shrink_node without a corresponding increment to scanned
> pages. Minchan Kim mentioned that this can also happen in
> the case of a THP page where the scanned is 1 and reclaimed
> could be 512.
> 
> Acked-by: Minchan Kim <minchan@kernel.org>
> Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>

Acked-by: Michal Hocko <mhocko@suse.com>

I would prefer the fixup in vmpressure() as already mentioned but this
should work as well.

> ---
> v2: Adding a comment and reordering the patches
>     as per Michal's suggestion
> 
>  mm/vmpressure.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
> index 149fdf6..6063581 100644
> --- a/mm/vmpressure.c
> +++ b/mm/vmpressure.c
> @@ -112,9 +112,16 @@ static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
>  						    unsigned long reclaimed)
>  {
>  	unsigned long scale = scanned + reclaimed;
> -	unsigned long pressure;
> +	unsigned long pressure = 0;
>  
>  	/*
> +	 * reclaimed can be greater than scanned in cases
> +	 * like THP, where the scanned is 1 and reclaimed
> +	 * could be 512
> +	 */
> +	if (reclaimed >= scanned)
> +		goto out;
> +	/*
>  	 * We calculate the ratio (in percents) of how many pages were
>  	 * scanned vs. reclaimed in a given time frame (window). Note that
>  	 * time is in VM reclaimer's "ticks", i.e. number of pages
> @@ -124,6 +131,7 @@ static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
>  	pressure = scale - (reclaimed * scale / scanned);
>  	pressure = pressure * 100 / scale;
>  
> +out:
>  	pr_debug("%s: %3lu  (s: %lu  r: %lu)\n", __func__, pressure,
>  		 scanned, reclaimed);
>  
> -- 
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
> member of the Code Aurora Forum, hosted by The Linux Foundation
> 

-- 
Michal Hocko
SUSE Labs

WARNING: multiple messages have this Message-ID
From: Michal Hocko <mhocko@kernel.org>
To: Vinayak Menon <vinmenon@codeaurora.org>
Cc: akpm@linux-foundation.org, hannes@cmpxchg.org,
	mgorman@techsingularity.net, vbabka@suse.cz, riel@redhat.com,
	vdavydov.dev@gmail.com, anton.vorontsov@linaro.org,
	minchan@kernel.org, shashim@codeaurora.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2 v2] mm: vmpressure: fix sending wrong events on underflow
Date: Thu, 9 Feb 2017 13:10:57 +0100	[thread overview]
Message-ID: <20170209121057.GF10257@dhcp22.suse.cz> (raw)
In-Reply-To: <1486641577-11685-1-git-send-email-vinmenon@codeaurora.org>

On Thu 09-02-17 17:29:36, Vinayak Menon wrote:
> At the end of a window period, if the reclaimed pages
> is greater than scanned, an unsigned underflow can
> result in a huge pressure value and thus a critical event.
> Reclaimed pages is found to go higher than scanned because
> of the addition of reclaimed slab pages to reclaimed in
> shrink_node without a corresponding increment to scanned
> pages. Minchan Kim mentioned that this can also happen in
> the case of a THP page where the scanned is 1 and reclaimed
> could be 512.
> 
> Acked-by: Minchan Kim <minchan@kernel.org>
> Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>

Acked-by: Michal Hocko <mhocko@suse.com>

I would prefer the fixup in vmpressure() as already mentioned but this
should work as well.

> ---
> v2: Adding a comment and reordering the patches
>     as per Michal's suggestion
> 
>  mm/vmpressure.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/vmpressure.c b/mm/vmpressure.c
> index 149fdf6..6063581 100644
> --- a/mm/vmpressure.c
> +++ b/mm/vmpressure.c
> @@ -112,9 +112,16 @@ static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
>  						    unsigned long reclaimed)
>  {
>  	unsigned long scale = scanned + reclaimed;
> -	unsigned long pressure;
> +	unsigned long pressure = 0;
>  
>  	/*
> +	 * reclaimed can be greater than scanned in cases
> +	 * like THP, where the scanned is 1 and reclaimed
> +	 * could be 512
> +	 */
> +	if (reclaimed >= scanned)
> +		goto out;
> +	/*
>  	 * We calculate the ratio (in percents) of how many pages were
>  	 * scanned vs. reclaimed in a given time frame (window). Note that
>  	 * time is in VM reclaimer's "ticks", i.e. number of pages
> @@ -124,6 +131,7 @@ static enum vmpressure_levels vmpressure_calc_level(unsigned long scanned,
>  	pressure = scale - (reclaimed * scale / scanned);
>  	pressure = pressure * 100 / scale;
>  
> +out:
>  	pr_debug("%s: %3lu  (s: %lu  r: %lu)\n", __func__, pressure,
>  		 scanned, reclaimed);
>  
> -- 
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
> member of the Code Aurora Forum, hosted by The Linux Foundation
> 

-- 
Michal Hocko
SUSE Labs

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

  parent reply	other threads:[~2017-02-09 12:23 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-02-09 11:59 Vinayak Menon
2017-02-09 11:59 ` Vinayak Menon
2017-02-09 11:59 ` [PATCH 2/2 v5] mm: vmscan: do not pass reclaimed slab to vmpressure Vinayak Menon
2017-02-09 11:59   ` Vinayak Menon
2017-02-09 12:20   ` Michal Hocko
2017-02-09 12:20     ` Michal Hocko
2017-02-10  8:45     ` vinayak menon
2017-02-10  8:45       ` vinayak menon
2017-02-10  9:05       ` Michal Hocko
2017-02-10  9:05         ` Michal Hocko
2017-02-09 12:10 ` Michal Hocko [this message]
2017-02-09 12:10   ` [PATCH 1/2 v2] mm: vmpressure: fix sending wrong events on underflow Michal Hocko
2017-02-09 12:22   ` Michal Hocko
2017-02-09 12:22     ` Michal Hocko

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20170209121057.GF10257@dhcp22.suse.cz \
    --to=mhocko@kernel.org \
    --cc=akpm@linux-foundation.org \
    --cc=anton.vorontsov@linaro.org \
    --cc=hannes@cmpxchg.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mgorman@techsingularity.net \
    --cc=minchan@kernel.org \
    --cc=riel@redhat.com \
    --cc=shashim@codeaurora.org \
    --cc=vbabka@suse.cz \
    --cc=vdavydov.dev@gmail.com \
    --cc=vinmenon@codeaurora.org \
    --subject='Re: [PATCH 1/2 v2] mm: vmpressure: fix sending wrong events on underflow' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.