linux-kernel - Re: [PATCH v1] mm:free unused pages in kmalloc

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Date:   Mon, 29 Jun 2020 14:48:06 +0000 (UTC)
From:   Christopher Lameter <cl@...ux.com>
To:     Long Li <lonuxli.64@...il.com>
cc:     penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] mm:free unused pages in kmalloc_order

On Sat, 27 Jun 2020, Long Li wrote:

> Environment using the slub allocator, 1G memory in my ARM32.
> kmalloc(1024, GFP_HIGHUSER) can allocate memory normally,
> kmalloc(64*1024, GFP_HIGHUSER) will cause a memory leak, because
> alloc_pages returns highmem physical pages, but it cannot be directly
> converted into a virtual address and return NULL, the pages has not
> been released. Usually driver developers will not use the
> GFP_HIGHUSER flag to allocate memory in kmalloc, but I think this
> memory leak is not perfect, it is best to be fixed. This is the
> first time I have posted a patch, there may be something wrong.

Highmem is not supported by the slab allocators. Please ensure that there
is a warning generated if someone attempts to do such an allocation. We
used to check for that.

In order to make such allocations possible one would have to create yet
another kmalloc array for high memory.