linux-kernel - Re: [PATCH v7 6/8] mm: zswap: Support mTHP swapout in zswap

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: <CAJD7tkYtVR6fi1R2O+jAxVfj7BJ2EKWbXHke9fkv_m=mf5pkFQ@mail.gmail.com>
Date: Wed, 25 Sep 2024 21:52:26 -0700
From: Yosry Ahmed <yosryahmed@...gle.com>
To: "Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
Cc: Johannes Weiner <hannes@...xchg.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, 
	"nphamcs@...il.com" <nphamcs@...il.com>, "chengming.zhou@...ux.dev" <chengming.zhou@...ux.dev>, 
	"usamaarif642@...il.com" <usamaarif642@...il.com>, "shakeel.butt@...ux.dev" <shakeel.butt@...ux.dev>, 
	"ryan.roberts@....com" <ryan.roberts@....com>, "Huang, Ying" <ying.huang@...el.com>, 
	"21cnbao@...il.com" <21cnbao@...il.com>, "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>, 
	"Zou, Nanhai" <nanhai.zou@...el.com>, "Feghali, Wajdi K" <wajdi.k.feghali@...el.com>, 
	"Gopal, Vinodh" <vinodh.gopal@...el.com>
Subject: Re: [PATCH v7 6/8] mm: zswap: Support mTHP swapout in zswap_store().

[..]
>
> One thing I realized while reworking the patches for the batched checks is:
> within zswap_store_page(), we set the entry->objcg and entry->pool before
> adding it to the xarray. Given this, wouldn't it be safer to get the objcg
> and pool reference per sub-page, locally in zswap_store_page(), rather than
> obtaining batched references at the end if the store is successful? If we want
> zswap_store_page() to be self-contained and correct as far as the entry
> being created and added to the xarray, it seems like the right thing to do?
> I am a bit apprehensive about the entry being added to the xarray without
> a reference obtained on the objcg and pool, because any page-faults/writeback
> that occur on sub-pages added to the xarray before the entire folio has been
> stored, would run into issues.

We definitely should not obtain references to the pool and objcg after
initializing the entries with them. We can obtain all references in
zswap_store() before zswap_store_page(). IOW, the batching in this
case should be done before the per-page operations, not after.

>
> Just wanted to run this by you. The rest of the batched charging, atomic
> and stat updates should be Ok.
>
> Thanks,
> Kanchana
>
> >
> > Thanks,
> > Kanchana