linux-kernel - Re: [PATCH v4 3/4] mm: Support batched unmap for lazyfree large folios during reclamation

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]

Message-ID: <CAGsJ_4woYd_TmZU94nedH=x_+HTwLxz94ih1jFmxoj4CxuhqzQ@mail.gmail.com>
Date: Thu, 26 Jun 2025 09:03:23 +1200
From: Barry Song <21cnbao@...il.com>
To: David Hildenbrand <david@...hat.com>
Cc: Lance Yang <lance.yang@...ux.dev>, akpm@...ux-foundation.org, 
	baolin.wang@...ux.alibaba.com, chrisl@...nel.org, kasong@...cent.com, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	linux-mm@...ck.org, linux-riscv@...ts.infradead.org, 
	lorenzo.stoakes@...cle.com, ryan.roberts@....com, v-songbaohua@...o.com, 
	x86@...nel.org, ying.huang@...el.com, zhengtangquan@...o.com, 
	Lance Yang <ioworker0@...il.com>
Subject: Re: [PATCH v4 3/4] mm: Support batched unmap for lazyfree large
 folios during reclamation

On Thu, Jun 26, 2025 at 12:25 AM David Hildenbrand <david@...hat.com> wrote:
>
> On 25.06.25 14:20, Lance Yang wrote:
[...]
> > Hmm... I have a question about the reference counting here ...
> >
> >               if (vma->vm_flags & VM_LOCKED)
> >                       mlock_drain_local();
> >               folio_put(folio);
> >               /* We have already batched the entire folio */
> >
> > Does anyone else still hold a reference to this folio after folio_put()?
>
> The caller of the unmap operation should better hold a reference :)
>
> Also, I am not sure why we don't perform a
>
> folio_put_refs(folio, nr_pages);

Because we've already called folio_ref_sub(folio, nr_pages - 1);
Looking back, it’s kind of ugly, huh.

discard:
                if (unlikely(folio_test_hugetlb(folio))) {
                        hugetlb_remove_rmap(folio);
                } else {
                        folio_remove_rmap_ptes(folio, subpage, nr_pages, vma);
                        folio_ref_sub(folio, nr_pages - 1);
                }

I assume Lance will send a patch? If so, remember to remove this
when switching to folio_put_refs(folio, nr_pages);

Thanks
Barry