Messages in this thread | | | From | "Chengang (L)" <> | Subject | Re: [PATCH] mm: align up min_free_kbytes to multipy of 4 | Date | Tue, 11 Jun 2019 12:10:36 +0000 |
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Hi Wei Yang
>On Sun, Jun 09, 2019 at 05:10:28PM +0800, ChenGang wrote: >>Usually the value of min_free_kbytes is multiply of 4, and in this case >>,the right shift is ok. >>But if it's not, the right-shifting operation will lose the low 2 bits,
>But PAGE_SHIFT is not always 12.
You are right, and this is not the key point, this is just an example.
>>and this cause kernel don't reserve enough memory. >>So it's necessary to align the value of min_free_kbytes to multiply of 4. >>For example, if min_free_kbytes is 64, then should keep 16 pages, but >>if min_free_kbytes is 65 or 66, then should keep 17 pages. >> >>Signed-off-by: ChenGang <cg.chen@huawei.com> >>--- >> mm/page_alloc.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >>diff --git a/mm/page_alloc.c b/mm/page_alloc.c index d66bc8a..1baeeba >>100644 >>--- a/mm/page_alloc.c >>+++ b/mm/page_alloc.c >>@@ -7611,7 +7611,8 @@ static void setup_per_zone_lowmem_reserve(void) >> >> static void __setup_per_zone_wmarks(void) { >>- unsigned long pages_min = min_free_kbytes >> (PAGE_SHIFT - 10); >>+ unsigned long pages_min = >>+ (PAGE_ALIGN(min_free_kbytes * 1024) / 1024) >> (PAGE_SHIFT - 10);
>In my mind, pages_min is an estimated value. Do we need to be so precise?
This is the key point, user can set this value through interface/proc/sys/vm/min_free_kbytes, so a bit more precise is better.
>> unsigned long lowmem_pages = 0; >> struct zone *zone; >> unsigned long flags; >>-- >>1.8.5.6
>-- >Wei Yang >Help you, Help me
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