linux-kernel - Re: [RFC PATCH] mm: khugepaged: don't carry huge page to the next loop for !CONFIG

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Date:   Wed, 1 Sep 2021 12:26:11 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Yang Shi <shy828301@...il.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     Hugh Dickins <hughd@...gle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] mm: khugepaged: don't carry huge page to the next
 loop for !CONFIG_NUMA

On 9/1/21 05:46, Yang Shi wrote:
> On Tue, Aug 31, 2021 at 4:38 PM Kirill A. Shutemov <kirill@...temov.name> wrote:
>>
>> On Mon, Aug 30, 2021 at 11:49:43AM -0700, Yang Shi wrote:
>> > Gently ping...
>> >
>> > Does this patch make sense? BTW, I have a couple of other khugepaged
>> > related patches in my queue. I plan to send them with this patch
>> > together. It would be great to hear some feedback before resending
>> > this one.
>>
>> I don't really care for !NUMA optimization. I believe that most of setups
>> that benefit from THP has NUMA enabled compile time.
> 
> Agreed.
> 
>>
>> But if you wanna to go this path, make an effort to cleanup other
>> artifacts for the !NUMA optimization: the ifdef has to be gone and all
>> callers of these helpers has to be revisited. There's more opportunities to
>> cleanup. Like it is very odd that khugepaged_prealloc_page() frees the
>> page.
> 
> Yes, they are gone in this patch. The only remaining for !NUMA is
> khugepaged_find_target_node() which just returns 0.

As Kirill pointed out, there's also khugepaged_prealloc_page() where the
only remaining variant does actually no preallocation, just freeing of an
unused page and some kind of "sleep after first alloc fail, break after
second alloc fail" logic.
This could now be moved to khugepaged_do_scan() loop itself and maybe it
will be easier to follow.

>>
>>
>> --
>>  Kirill A. Shutemov
>