From: yangerkun <yangerkun@huawei.com>
To: Matthew Wilcox <willy@infradead.org>,
Greg KH <gregkh@linuxfoundation.org>, <joe@perches.com>
Cc: <stable@vger.kernel.org>, <vbabka@suse.cz>, <linux-mm@kvack.org>,
<open-iscsi@googlegroups.com>, <cleech@redhat.com>,
"zhangyi (F)" <yi.zhang@huawei.com>,
Kefeng Wang <wangkefeng.wang@huawei.com>,
<liuyongqiang13@huawei.com>,
"Zhengyejian (Zetta)" <zhengyejian1@huawei.com>,
Yang Yingliang <yangyingliang@huawei.com>,
<chenzhou10@huawei.com>
Subject: Re: [QUESTION] WARNNING after 3d8e2128f26a ("sysfs: Add sysfs_emit and sysfs_emit_at to format sysfs output")
Date: Wed, 7 Apr 2021 20:14:52 +0800 [thread overview]
Message-ID: <08b739b5-4401-e550-2028-1ce43db38141@huawei.com> (raw)
In-Reply-To: <20210402144120.GO351017@casper.infradead.org>
在 2021/4/2 22:41, Matthew Wilcox 写道:
> On Fri, Apr 02, 2021 at 09:45:12AM +0200, Greg KH wrote:
>> Why is the buffer alignment considered a "waste" here? If that change
>> is in Linus's tree and newer kernels (it showed up in 5.4 which was
>> released quite a while ago), where are the people complaining about it
>> there?
>>
>> I think backporting 59bb47985c1d ("mm, sl[aou]b: guarantee natural
>> alignment for kmalloc(power-of-two)") seems like the correct thing to do
>> here to bring things into alignment (pun intended) with newer kernels.
>
> It's only a waste for slabs which need things like redzones (eg we could
> get 7 512-byte allocations out of a 4kB page with a 64 byte redzone
> and no alignment ; with alignment we can only get four). Since slub
> can enable/disable redzones on a per-slab basis, and redzones aren't
> terribly interesting now that we have kasan/kfence, nobody really cares.
>
> .
>
Thanks for your explain! The imfluence seems minimal since the "waste"
will happen only when we enable slub_debug.
One more question for Joe Perches. Patch v2[1] does not add the
alignment check for buf and we add it in v3[2]. I don't see the
necessity for this check... Can you help to explain that why we need this?
Thanks,
Kun.
[1].
https://lore.kernel.org/lkml/a9054fb521e65f2809671fa9c18e2453061e9d91.1598744610.git.joe@perches.com/
[2].
https://lore.kernel.org/lkml/743a648dc817cddd2e7046283c868f1c08742f29.camel@perches.com/
next prev parent reply other threads:[~2021-04-07 12:15 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-02 7:16 yangerkun
2021-04-02 7:24 ` yangerkun
2021-04-02 7:45 ` Greg KH
2021-04-02 14:41 ` Matthew Wilcox
2021-04-07 12:14 ` yangerkun [this message]
2021-04-07 13:21 ` Joe Perches
2021-04-07 13:49 ` yangerkun
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