linux-kernel - Re: [PATCH v2] mm: align larger anonymous mappings on THP boundaries

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Date: Thu, 18 Jan 2024 08:04:56 +0100
From: Jiri Slaby <jirislaby@...nel.org>
To: Yang Shi <shy828301@...il.com>
Cc: Rik van Riel <riel@...riel.com>, Andrew Morton
 <akpm@...ux-foundation.org>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, kernel-team@...com,
 Matthew Wilcox <willy@...radead.org>, Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH v2] mm: align larger anonymous mappings on THP boundaries

On 18. 01. 24, 1:07, Yang Shi wrote:
>> This works around the problem, of course (but is a band-aid, not a fix):
>>
>> --- a/mm/mmap.c
>> +++ b/mm/mmap.c
>> @@ -1829,7 +1829,7 @@ get_unmapped_area(struct file *file, unsigned long
>> addr, unsigned long len,
>>                    */
>>                   pgoff = 0;
>>                   get_area = shmem_get_unmapped_area;
>> -       } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
>> +       } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
>> !in_32bit_syscall()) {
>>                   /* Ensures that larger anonymous mappings are THP
>> aligned. */
>>                   get_area = thp_get_unmapped_area;
>>           }
>>
>>
>> thp_get_unmapped_area() does not take care of the legacy stuff...
> 
> Could you please help test the below patch? It is compiled, but I
> don't have 32 bit userspace or machine to test it.

Yeah, for x86_64, it's semantically the same as the above, so this works 
too:

Tested-by: Jiri Slaby <jirislaby@...nel.org>

> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -811,6 +811,9 @@ static unsigned long
> __thp_get_unmapped_area(struct file *filp,
>          loff_t off_align = round_up(off, size);
>          unsigned long len_pad, ret;
> 
> +       if (IS_ENABLED(CONFIG_32BIT) || in_compat_syscall())
> +               return 0;
> +
>          if (off_end <= off_align || (off_end - off_align) < size)
>                  return 0;

thanks,
-- 
js
suse labs