linux-kernel - Re: [PATCH] mm: huge_memory: don't force huge page alignment on 32 bit

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Date: Fri, 26 Jan 2024 10:36:53 +0100
From: Jiri Slaby <jirislaby@...nel.org>
To: akpm@...ux-foundation.org
Cc: surenb@...gle.com, riel@...riel.com, willy@...radead.org, cl@...ux.com,
 yang@...amperecomputing.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, "Bernhard M. Wiedemann" <bwiedemann@...e.de>,
 Michal Hocko <mhocko@...e.com>, Yang Shi <shy828301@...il.com>
Subject: Re: [PATCH] mm: huge_memory: don't force huge page alignment on 32
 bit

On 25. 01. 24, 9:53, Michal Hocko wrote:
> On Thu 18-01-24 05:35:04, Yang Shi wrote:
>> From: Yang Shi <yang@...amperecomputing.com>
>>
>> The commit efa7df3e3bb5 ("mm: align larger anonymous mappings on THP
>> boundaries") caused two issues [1] [2] reported on 32 bit system or compat
>> userspace.
>>
>> It doesn't make too much sense to force huge page alignment on 32 bit
>> system due to the constrained virtual address space.
>>
>> [1] https://lore.kernel.org/linux-mm/CAHbLzkqa1SCBA10yjWTtA2mKCsoK5+M1BthSDL8ROvUq2XxZMw@mail.gmail.com/T/#mf211643a0427f8d6495b5b53f8132f453d60ab95
>> [2] https://lore.kernel.org/linux-mm/CAHbLzkqa1SCBA10yjWTtA2mKCsoK5+M1BthSDL8ROvUq2XxZMw@mail.gmail.com/T/#me93dff2ccbd9902c3e395e1c022fb454e48ecb1d
>>
>> Fixes: efa7df3e3bb5 ("mm: align larger anonymous mappings on THP boundaries")
>> Reported-by: Jiri Slaby <jirislaby@...nel.org>
>> Reported-by: Suren Baghdasaryan <surenb@...gle.com>
>> Tested-by: Jiri Slaby <jirislaby@...nel.org>
>> Tested-by: Suren Baghdasaryan <surenb@...gle.com>
>> Cc: Rik van Riel <riel@...riel.com>
>> Cc: Matthew Wilcox <willy@...radead.org>
>> Cc: Christopher Lameter <cl@...ux.com>
>> Signed-off-by: Yang Shi <yang@...amperecomputing.com>
> 
> Acked-by: Michal Hocko <mhocko@...e.com>
> 
> Thanks!
> 
>> ---
>>   mm/huge_memory.c | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index 94ef5c02b459..e9fbaccbe0c0 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -37,6 +37,7 @@
>>   #include <linux/page_owner.h>
>>   #include <linux/sched/sysctl.h>
>>   #include <linux/memory-tiers.h>
>> +#include <linux/compat.h>
>>   
>>   #include <asm/tlb.h>
>>   #include <asm/pgalloc.h>
>> @@ -811,6 +812,14 @@ static unsigned long __thp_get_unmapped_area(struct file *filp,
>>   	loff_t off_align = round_up(off, size);
>>   	unsigned long len_pad, ret;
>>   
>> +	/*
>> +	 * It doesn't make too much sense to froce huge page alignment on
>> +	 * 32 bit system or compat userspace due to the contrained virtual
>> +	 * address space and address entropy.
>> +	 */

FWIW,
Bernhard noticed that "froce" and "contrained", could you fix that 
before applying the patch?

thanks,
-- 
js
suse labs