linux-kernel - Re: [RFC PATCH v2] mm/vmalloc: fix incorrect __vmap_pages_range_noflush() if vm_area_alloc_pages() from high order fallback to order0

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Message-ID: <20240730032447.avaoa5uhcxdkcjzs@oppo.com>
Date: Tue, 30 Jul 2024 11:24:47 +0800
From: Hailong Liu <hailong.liu@...o.com>
To: Baoquan He <bhe@...hat.com>
CC: Barry Song <21cnbao@...il.com>, Andrew Morton <akpm@...ux-foundation.org>,
	Uladzislau Rezki <urezki@...il.com>, Christoph Hellwig <hch@...radead.org>,
	Lorenzo Stoakes <lstoakes@...il.com>, Vlastimil Babka <vbabka@...e.cz>,
	Michal Hocko <mhocko@...e.com>, Matthew Wilcox <willy@...radead.org>,
	Tangquan Zheng <zhengtangquan@...o.com>, <linux-mm@...ck.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2] mm/vmalloc: fix incorrect
 __vmap_pages_range_noflush() if vm_area_alloc_pages() from high order
 fallback to order0

On Mon, 29. Jul 09:48, Baoquan He wrote:
[...]
> Hi Hailong,
>
> Please feel free to collect them to post formal patch, maybe two
> patches, one is to allow non-nofail to fallback to order-0 in
> vm_area_alloc_pages(), the other is passing out the fallbacked
> page_order to vmap_pages_range() if it's OK.
Sorry for late response. I personally prefer to revert part of
the problematic patch. There are several reasons:
- Save memory usage if high order allocation failed.
- If nofail and fallback to order0 in vmalloc huge allocation,
actually the allocation is alighed with PMD_SIZE or not PAGE_SHIFT.

You might be concerned about performance issues. But IMO,
- If we fallback to order0, we can make use of bulk allocator.
- Maybe we can remove VM_ALLOW_HUGE_VMAP in kvmalloc.

I am not sure if I have misunderstood anything. If I have, please
let me know.
>
> Thanks
> Baoquan
>
>

--
help you, help me,
Hailong.