linux-kernel - Re: [PATCH v4 4/7] x86/tlb: fall back to flush all when meet a THP large page

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Message-ID: <4FAE1808.1080504@intel.com>
Date:	Sat, 12 May 2012 15:58:00 +0800
From:	Alex Shi <alex.shi@...el.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
CC:	rob@...dley.net, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, arnd@...db.de, rostedt@...dmis.org,
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Subject: Re: [PATCH v4 4/7] x86/tlb: fall back to flush all when meet a THP
 large page

On 05/12/2012 12:28 AM, Andrea Arcangeli wrote:

> Hi,
> 
> On Thu, May 10, 2012 at 01:00:10PM +0800, Alex Shi wrote:
>> +	for (addr = start; addr <= end; addr += HPAGE_SIZE) {
>> +		pgd = pgd_offset(mm, addr);
>> +		if (likely(!pgd_none(*pgd))) {
>> +			pud = pud_offset(pgd, addr);
>> +			if (likely(!pud_none(*pud))) {
>> +				pmd = pmd_offset(pud, addr);
>> +				if (likely(!pmd_none(*pmd)))
>> +					if (pmd_large(*pmd))
>> +						return 1;
> 
> Note with THP we've to set the pmd temporarily not present during
> split_huge_page just before it returns a regular pmd (to avoid erratas
> and mixing 4k and 2m tlb on the same physical page). So pmd_large
> would fail in that small time window and we would do the invlpg loop
> (which should still work safe so no big deal). But I believe you could
> use pmd_trans_huge above, maybe gcc can drop the whole block with
> CONFIG_TRANSPARENT_HUGEPAGE=n.


Thanks the explanation.
Sure, if THP was not enabled, we can return 0 directly. :)
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