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From: Xishi Qiu <qiuxishi@huawei.com>
To: Linux MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>
Subject: why not add __GFP_HIGHMEM directly in alloc_migrate_target()?
Date: Tue, 12 Jul 2016 21:16:07 +0800	[thread overview]
Message-ID: <5784ED97.1080807@huawei.com> (raw)

alloc_migrate_target() is called from migrate_pages(),
so the page is always from user space, so why not add
__GFP_HIGHMEM directly, instead of the following code.

	if (PageHighMem(page))  // it always return false in x86_64
		gfp_mask |= __GFP_HIGHMEM;


Another question, when we do migration, why should split THP
first?
e.g. 2M(512*4kb) should flush 512 times TLB, and 2M(2M*1) only need one. 
I find flush TLB takes a lot of time, especially multithreaded app.

Thanks,
Xishi Qiu

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WARNING: multiple messages have this Message-ID (diff)
From: Xishi Qiu <qiuxishi@huawei.com>
To: Linux MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>
Subject: why not add __GFP_HIGHMEM directly in alloc_migrate_target()?
Date: Tue, 12 Jul 2016 21:16:07 +0800	[thread overview]
Message-ID: <5784ED97.1080807@huawei.com> (raw)

alloc_migrate_target() is called from migrate_pages(),
so the page is always from user space, so why not add
__GFP_HIGHMEM directly, instead of the following code.

	if (PageHighMem(page))  // it always return false in x86_64
		gfp_mask |= __GFP_HIGHMEM;


Another question, when we do migration, why should split THP
first?
e.g. 2M(512*4kb) should flush 512 times TLB, and 2M(2M*1) only need one. 
I find flush TLB takes a lot of time, especially multithreaded app.

Thanks,
Xishi Qiu

             reply	other threads:[~2016-07-12 13:33 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-07-12 13:16 Xishi Qiu [this message]
2016-07-12 13:16 ` why not add __GFP_HIGHMEM directly in alloc_migrate_target()? Xishi Qiu

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