linux-kernel - Re: [PATCH] mm: make __GFP_SKIP_ZERO visible to skip zero operation

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Message-ID: <ZPWH53NUqTIoDcMV@dhcp22.suse.cz>
Date:   Mon, 4 Sep 2023 09:31:51 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Zhaoyang Huang <huangzhaoyang@...il.com>
Cc:     Matthew Wilcox <willy@...radead.org>, glider@...gle.com,
        "zhaoyang.huang" <zhaoyang.huang@...soc.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, ke.wang@...soc.com
Subject: Re: [PATCH] mm: make __GFP_SKIP_ZERO visible to skip zero operation

On Fri 01-09-23 18:29:07, Zhaoyang Huang wrote:
> loop alex
> 
> On Thu, Aug 31, 2023 at 8:16 PM Matthew Wilcox <willy@...radead.org> wrote:
> >
> > On Thu, Aug 31, 2023 at 06:52:52PM +0800, zhaoyang.huang wrote:
> > > From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> > >
> > > There is no explicit gfp flags to let the allocation skip zero
> > > operation when CONFIG_INIT_ON_ALLOC_DEFAULT_ON=y. I would like to make
> > > __GFP_SKIP_ZERO be visible even if kasan is not configured.
> >
> > This bypasses a security feature so you're going to have to do a little
> > better than "I want it".
> Thanks for pointing this out. What I want to do is to give the user a
> way to exempt some types of pages from being zeroed, which could help
> on performance issues.

Could you be more explicit about those users? Your patch doesn't add
any.

> Could we have the most safety concern admin
> use INIT_ON_FREE while the less concerned use INIT_ON_ALLOC &
> __GFP_SKIP_ZERO as a light version method?

Are you suggesting the __GFP_SKIP_ZERO would be ignored in any setups
except for init_on_alloc?

-- 
Michal Hocko
SUSE Labs