Subject: Re: [RFC] mm: why vfree() do not free page table memory?
To: Xishi Qiu <qiuxishi@huawei.com>, Michal Hocko <mhocko@kernel.org>,
        Mel Gorman <mgorman@techsingularity.net>
Cc: LKML <linux-kernel@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
        "Wujiangtao (A)" <wu.wujiangtao@huawei.com>
References: <5A4603AB.8060809@huawei.com>
From: Vlastimil Babka <vbabka@suse.cz>
Message-ID: <0ffd113e-84da-bd49-2b63-3d27d2702580@suse.cz>
Date: Wed, 17 Jan 2018 10:16:01 +0100
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On 12/29/2017 09:58 AM, Xishi Qiu wrote:
> When calling vfree(), it calls unmap_vmap_area() to clear page table,
> but do not free the memory of page table, why? just for performance?

I guess it's expected that the free virtual range and associated page
tables it might be reused later.

> If a driver use vmalloc() and vfree() frequently, we will lost much
> page table memory, maybe oom later.

If it's reused, then not really.

Did you notice an actual issue, or is this just theoretical concern.

> Thanks,
> Xishi Qiu
>