linux-kernel - Re: [PATCH v9 1/8] hugetlb_cgroup: Add hugetlb

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Message-ID: <CAHS8izMT2vNASsR2H+3-4XN=+EkAEpS-LJ_UouaAa7iUfbLBhQ@mail.gmail.com>
Date:   Mon, 13 Jan 2020 14:21:33 -0800
From:   Mina Almasry <almasrymina@...gle.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     shuah <shuah@...nel.org>, David Rientjes <rientjes@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        open list <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org, cgroups@...r.kernel.org,
        Aneesh Kumar <aneesh.kumar@...ux.vnet.ibm.com>,
        Michal Koutný <mkoutny@...e.com>,
        Hillf Danton <hdanton@...a.com>
Subject: Re: [PATCH v9 1/8] hugetlb_cgroup: Add hugetlb_cgroup reservation counter

> >> On 12/17/19 3:16 PM, Mina Almasry wrote:
> >
> > The design we went with based on previous discussions is as follows:
> > hugetlb pages faulted without a prior reservation get accounted at
> > fault time, rather than reservation time, and if the fault causes the
> > counter to cross the limit, the charge fails, hence the fault fails,
> > hence the process gets sigbus'd.
>
> Ok, sorry I did not recall the design discussion.
>

No worries! It has indeed been a while since that discussion.

> > This means that one counter I'm adding here can cover both use cases:
> > if the userspace uses MAP_NORESERVE, then their memory is accounted at
> > fault time and they may get sigbus'd.
>
> Let's make sure this is clearly documented.  Someone could be surprised
> if their application not using reserves gets a SIGBUS because there is a
> reserve limit.

I have some stuff on that already in the docs patch, but I'll beef
that section up to ensure there is no confusion.