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 12:16:35 +0000 |
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Hi Michal
>On Sun 09-06-19 17:10:28, 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, 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.
>Could you describe the actual problem? Do we ever generate min_free_kbytes that would lead to unexpected reserves or is this trying to compensate for those values being configured from the userspace? If later why do we care at all?
>Have you seen this to be an actual problem or is this mostly motivated by the code reading?
I haven't seen an actual problem, and it's motivated by code reading. Users can configure this value through interface /proc/sys/vm/min_free_kbytes, so I think a bit precious is better.
>> 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); >> unsigned long lowmem_pages = 0; >> struct zone *zone; >> unsigned long flags; >> -- >> 1.8.5.6 >>
>-- >Michal Hocko >SUSE Labs
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