linux-kernel - Re: [PATCH 20/28] mm, swap: check swap table directly for checking cache

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] [day] [month] [year] [list]

Message-ID: <aFUWKzlSD9GKPuP/@MiWiFi-R3L-srv>
Date: Fri, 20 Jun 2025 16:04:59 +0800
From: Baoquan He <bhe@...hat.com>
To: Kairui Song <ryncsn@...il.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Wilcox <willy@...radead.org>,
	Hugh Dickins <hughd@...gle.com>, Chris Li <chrisl@...nel.org>,
	David Hildenbrand <david@...hat.com>,
	Yosry Ahmed <yosryahmed@...gle.com>,
	"Huang, Ying" <ying.huang@...ux.alibaba.com>,
	Nhat Pham <nphamcs@...il.com>, Johannes Weiner <hannes@...xchg.org>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Barry Song <baohua@...nel.org>,
	Kalesh Singh <kaleshsingh@...gle.com>,
	Kemeng Shi <shikemeng@...weicloud.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Ryan Roberts <ryan.roberts@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 20/28] mm, swap: check swap table directly for checking
 cache

On 06/19/25 at 06:50pm, Kairui Song wrote:
> On Thu, Jun 19, 2025 at 6:38 PM Baoquan He <bhe@...hat.com> wrote:
> >
> > On 05/15/25 at 04:17am, Kairui Song wrote:
> > > From: Kairui Song <kasong@...cent.com>
> > >
> > > Instead of looking at the swap map, check swap table directly to tell if
> > > a swap entry has cache. Prepare for remove SWAP_HAS_CACHE.
> >
> > But you actually check both the swap table entry and swap map entry in
> > this patch, or do I miss anything?
> 
> Hi, Baoquan
> 
> >
> > E.g
> >
> > if (!swap_count(si->swap_map[offset]) && swp_te_is_folio(swp_te))
> 
> Yes, the count info is still in the swap_map now, I'm only converting
> the HAS_CACHE check to use swp_te_t here. We'll remove swap_map in
> later patches and use the swp_te_t solely to get both info.

Ah, I see it now. That's why the subject is saying it's checking swap table
for checking cache. Then it's fine to me, even though it's a little
confusing. 

> 
> The reason some checks are added to check the swap_count is that:
> Before this patch, `swap_map[offset] == SWAP_HAS_CACHE` implies the
> count is zero too. So if HAS_CACHE is moved to swp_te_t, we still need
> to check the count separately. The overhead will be gone very soon in
> a later patch.

Got it, that sounds great, thanks.