linux-kernel - [RFC] mm: why vfree() do not free page table memory?

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Message-ID: <5A4603AB.8060809@huawei.com>
Date:   Fri, 29 Dec 2017 16:58:19 +0800
From:   Xishi Qiu <qiuxishi@...wei.com>
To:     Michal Hocko <mhocko@...nel.org>, Vlastimil Babka <vbabka@...e.cz>,
        "Mel Gorman" <mgorman@...hsingularity.net>
CC:     LKML <linux-kernel@...r.kernel.org>, Linux MM <linux-mm@...ck.org>,
        "Xishi Qiu" <qiuxishi@...wei.com>,
        "Wujiangtao (A)" <wu.wujiangtao@...wei.com>
Subject: [RFC] mm: why vfree() do not free page table memory?

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?

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

Thanks,
Xishi Qiu