linux-kernel - Re: [PATCH 1/1] mm/khugepaged: skip copying lazyfree pages on collapse

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date: Fri, 2 Feb 2024 19:18:31 +0800
From: Lance Yang <ioworker0@...il.com>
To: Michal Hocko <mhocko@...e.com>
Cc: akpm@...ux-foundation.org, zokeefe@...gle.com, david@...hat.com, 
	songmuchun@...edance.com, shy828301@...il.com, peterx@...hat.com, 
	minchan@...nel.org, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] mm/khugepaged: skip copying lazyfree pages on collapse

On Fri, Feb 2, 2024 at 6:06 PM Michal Hocko <mhocko@...e.com> wrote:
>
> On Thu 01-02-24 20:52:26, Lance Yang wrote:
> > The collapsing behavior of khugepaged with pages
> > marked using MADV_FREE might cause confusion
> > among users.
> >
> > For instance, allocate a 2MB chunk using mmap and
> > later release it by MADV_FREE. Khugepaged will not
> > collapse this chunk. From the user's perspective,
> > it treats lazyfree pages as pte_none. However,
> > for some pages marked as lazyfree with MADV_FREE,
> > khugepaged might collapse this chunk and copy
> > these pages to a new huge page. This inconsistency
> > in behavior could be confusing for users.
>
> Is that any more confusing than collapsing pte_none
> pages?
>
> TBH I do not really see why this is a problem. MADV_FREE
> are correctly recognized same as pte_none so the user
> defined trashold applies.

Sorry, I might not have expressed it clearly.
MADV_FREE is correctly recognized, just like
pte_none. This is also reasonable and not an issue.

IMO, since it's treated the same as pte_none,
perhaps lazyfree pages shouldn't be copied to
the new huge page.

Thanks,
Lance
> --
> Michal Hocko
> SUSE Labs