From: Matthew Wilcox <willy@infradead.org>
To: Christopher Lameter <cl@linux.com>
Cc: Long Li <lonuxli.64@gmail.com>,
penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com,
akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1] mm:free unused pages in kmalloc_order
Date: Mon, 29 Jun 2020 15:52:59 +0100 [thread overview]
Message-ID: <20200629145259.GD25523@casper.infradead.org> (raw)
In-Reply-To: <alpine.DEB.2.22.394.2006291446560.27163@www.lameter.com>
On Mon, Jun 29, 2020 at 02:48:06PM +0000, Christopher Lameter wrote:
> 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.
Sounds like we need a test somewhere that checks this behaviour.
> In order to make such allocations possible one would have to create yet
> another kmalloc array for high memory.
Not for this case because it goes straight to kmalloc_order(). What does
make this particular case impossible is that we can't kmap() a compound
page. We could vmap it, but why are we bothering?
next prev parent reply other threads:[~2020-06-29 14:53 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-27 4:55 [PATCH v1] mm:free unused pages in kmalloc_order Long Li
2020-06-29 2:42 ` Matthew Wilcox
2020-06-29 14:49 ` Christopher Lameter
2020-06-29 14:48 ` Christopher Lameter
2020-06-29 14:52 ` Matthew Wilcox [this message]
2020-07-01 15:18 ` Christopher Lameter
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