* [PATCH] mm: Set min_free_kbytes with user_min_free_kbytes when user_min_free_kbytes is preferred
@ 2021-09-28 12:23 Liangcai Fan
2021-09-28 22:29 ` Andrew Morton
0 siblings, 1 reply; 3+ messages in thread
From: Liangcai Fan @ 2021-09-28 12:23 UTC (permalink / raw)
To: liangcai.fan, akpm; +Cc: linux-kernel, linux-mm, zhang.lyra, Liangcai Fan
The 'min_free_kbytes' and 'user_min_free_kbytes' maybe inconsistent
after a few times of memory hotplug.
When 'new_min_free_kbytes' is not larger than 'user_min_free_kbytes',
set 'min_free_kbytes' with 'user_min_free_kbytes' rather than leave
it as the 'new_min_free_kbytes' calculated for the last time.
Signed-off-by: Liangcai Fan <liangcaifan19@gmail.com>
Cc: Chunyan Zhang <zhang.lyra@gmail.com>
---
mm/page_alloc.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b37435c..ddf9dc1 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8467,6 +8467,12 @@ int __meminit init_per_zone_wmark_min(void)
if (min_free_kbytes > 262144)
min_free_kbytes = 262144;
} else {
+ /*
+ * Set 'min_free_kbytes' with 'user_min_free_kbytes' rather than
+ * leave it as the 'new_min_free_kbytes' calculated for the last
+ * time.
+ */
+ min_free_kbytes = user_min_free_kbytes;
pr_warn("min_free_kbytes is not updated to %d because user defined value %d is preferred\n",
new_min_free_kbytes, user_min_free_kbytes);
}
--
1.9.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] mm: Set min_free_kbytes with user_min_free_kbytes when user_min_free_kbytes is preferred
2021-09-28 12:23 [PATCH] mm: Set min_free_kbytes with user_min_free_kbytes when user_min_free_kbytes is preferred Liangcai Fan
@ 2021-09-28 22:29 ` Andrew Morton
2021-09-29 6:15 ` Fan Liangcai
0 siblings, 1 reply; 3+ messages in thread
From: Andrew Morton @ 2021-09-28 22:29 UTC (permalink / raw)
To: Liangcai Fan; +Cc: liangcai.fan, linux-kernel, linux-mm, zhang.lyra
On Tue, 28 Sep 2021 20:23:17 +0800 Liangcai Fan <liangcaifan19@gmail.com> wrote:
> The 'min_free_kbytes' and 'user_min_free_kbytes' maybe inconsistent
> after a few times of memory hotplug.
What does "inconsistent" mean here?
Please describe the problem in more detail, perhaps with examples.
> When 'new_min_free_kbytes' is not larger than 'user_min_free_kbytes',
> set 'min_free_kbytes' with 'user_min_free_kbytes' rather than leave
> it as the 'new_min_free_kbytes' calculated for the last time.
>
> Signed-off-by: Liangcai Fan <liangcaifan19@gmail.com>
> Cc: Chunyan Zhang <zhang.lyra@gmail.com>
> ---
> mm/page_alloc.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b37435c..ddf9dc1 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8467,6 +8467,12 @@ int __meminit init_per_zone_wmark_min(void)
> if (min_free_kbytes > 262144)
> min_free_kbytes = 262144;
> } else {
> + /*
> + * Set 'min_free_kbytes' with 'user_min_free_kbytes' rather than
> + * leave it as the 'new_min_free_kbytes' calculated for the last
> + * time.
> + */
This comment explains what the code is doing, which is almost always
obvious from reading the code! A better comment will describe *why*
the code is doing whatever is does. "why, not what", please.
> + min_free_kbytes = user_min_free_kbytes;
> pr_warn("min_free_kbytes is not updated to %d because user defined value %d is preferred\n",
> new_min_free_kbytes, user_min_free_kbytes);
> }
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] mm: Set min_free_kbytes with user_min_free_kbytes when user_min_free_kbytes is preferred
2021-09-28 22:29 ` Andrew Morton
@ 2021-09-29 6:15 ` Fan Liangcai
0 siblings, 0 replies; 3+ messages in thread
From: Fan Liangcai @ 2021-09-29 6:15 UTC (permalink / raw)
To: Andrew Morton; +Cc: liangcai.fan, linux-kernel, linux-mm, Chunyan Zhang
Andrew Morton <akpm@linux-foundation.org> 于2021年9月29日周三 上午6:29写道:
>
> On Tue, 28 Sep 2021 20:23:17 +0800 Liangcai Fan <liangcaifan19@gmail.com> wrote:
>
> > The 'min_free_kbytes' and 'user_min_free_kbytes' maybe inconsistent
> > after a few times of memory hotplug.
>
> What does "inconsistent" mean here?
>
> Please describe the problem in more detail, perhaps with examples.
>
example:
1. Turn on the device with 1G memory, and the calculated 'new_min_free_kbytes'
is 3452kb, at this time 'min_free_kbytes' = 'new_min_free_kbytes' = 3452kb,
'user_min_free_kbytes' is the initial value -1.
2. The user sets 'min_free_kbytes' to 4096kb through the node,
at this time 'user_min_free_kbytes' = 'min_free_kbytes' = 4096kb.
3. The memory has increased by 2G, and the memory has become 3G.
Recalculate 'new_min_free_kbytes' to be 6568kb, which is greater than
'user_min_free_kbytes'(4096kb), at this time
'min_free_kbytes' = 'new_min_free_kbytes' = 6568kb,
'user_min_free_kbytes' = 4096kb.
4. The memory has been reduced by 2G, and now the memory has become 1G.
Recalculate 'new_min_free_kbytes' to be 3452kb, which is less than
'user_min_free_kbytes'(4096kb). The original logic does not modify
'min_free_kbytes'.
At this time, 'min_free_kbytes' is the last 'new_min_free_kbytes'(6568kb).
The memory is 1G ,'min_free_kbytes' should be equal to
'user_min_free_kbytes'(4096kb)
set by the user.
> > When 'new_min_free_kbytes' is not larger than 'user_min_free_kbytes',
> > set 'min_free_kbytes' with 'user_min_free_kbytes' rather than leave
> > it as the 'new_min_free_kbytes' calculated for the last time.
> >
> > Signed-off-by: Liangcai Fan <liangcaifan19@gmail.com>
> > Cc: Chunyan Zhang <zhang.lyra@gmail.com>
> > ---
> > mm/page_alloc.c | 6 ++++++
> > 1 file changed, 6 insertions(+)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index b37435c..ddf9dc1 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -8467,6 +8467,12 @@ int __meminit init_per_zone_wmark_min(void)
> > if (min_free_kbytes > 262144)
> > min_free_kbytes = 262144;
> > } else {
> > + /*
> > + * Set 'min_free_kbytes' with 'user_min_free_kbytes' rather than
> > + * leave it as the 'new_min_free_kbytes' calculated for the last
> > + * time.
> > + */
>
> This comment explains what the code is doing, which is almost always
> obvious from reading the code! A better comment will describe *why*
> the code is doing whatever is does. "why, not what", please.
>
I think this comment is redundant and will be deleted.
> > + min_free_kbytes = user_min_free_kbytes;
> > pr_warn("min_free_kbytes is not updated to %d because user defined value %d is preferred\n",
> > new_min_free_kbytes, user_min_free_kbytes);
> > }
>
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2021-09-29 6:16 UTC | newest]
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2021-09-28 12:23 [PATCH] mm: Set min_free_kbytes with user_min_free_kbytes when user_min_free_kbytes is preferred Liangcai Fan
2021-09-28 22:29 ` Andrew Morton
2021-09-29 6:15 ` Fan Liangcai
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