linux-kernel - Re: [v3 2/3] mm: Defer TLB flush by keeping both src and dst folios at migration

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Message-ID: <0138328C-74D5-471E-A2CC-7675CA692F42@vmware.com>
Date:   Mon, 30 Oct 2023 15:58:44 +0000
From:   Nadav Amit <namit@...are.com>
To:     Byungchul Park <byungchul@...com>
CC:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        "kernel_team@...ynix.com" <kernel_team@...ynix.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "ying.huang@...el.com" <ying.huang@...el.com>,
        "xhao@...ux.alibaba.com" <xhao@...ux.alibaba.com>,
        "mgorman@...hsingularity.net" <mgorman@...hsingularity.net>,
        "hughd@...gle.com" <hughd@...gle.com>,
        "willy@...radead.org" <willy@...radead.org>,
        "david@...hat.com" <david@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
Subject: Re: [v3 2/3] mm: Defer TLB flush by keeping both src and dst folios
 at migration



> On Oct 30, 2023, at 2:51 PM, Byungchul Park <byungchul@...com> wrote:
> 
> I really spent a lot of time hesitating whether splitting it or not.
> However, the test result cannot be stable without those. I'm still
> confused. I think the test result should be stable at each commit,
> right?

Of course. You can extract the optimization we mentioned, and perhaps
have more preparatory patches.

Just a couple of comments that may also help breaking the patches:

1. The “stopping” logic is a bit not great. Try to see if you can
somehow use shrinker or OOM infrastructure instead.

2. Regarding “overflows”, it’s not always a question of whether an
overflow would happen naturally, but whether a malicious process can
trigger it.

Regards,
Nadav