linux-kernel - Re: [PATCH v8 04/10] mm: thp: Support allocation of anonymous multi-size THP

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Message-ID: <1370c5b7-c914-4861-ad7a-90199723994a@redhat.com>
Date:   Tue, 5 Dec 2023 17:35:20 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Ryan Roberts <ryan.roberts@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Yin Fengwei <fengwei.yin@...el.com>,
        Yu Zhao <yuzhao@...gle.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Yang Shi <shy828301@...il.com>,
        "Huang, Ying" <ying.huang@...el.com>, Zi Yan <ziy@...dia.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Itaru Kitayama <itaru.kitayama@...il.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        John Hubbard <jhubbard@...dia.com>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Hugh Dickins <hughd@...gle.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Barry Song <21cnbao@...il.com>,
        Alistair Popple <apopple@...dia.com>
Cc:     linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 04/10] mm: thp: Support allocation of anonymous
 multi-size THP

> Comment: Both will eventually loop over all orders, correct? Could
> eventually be sped up in the future.
> 
> Nit: the orders = ... order = ... looks like this might deserve a helper
> function that makes this easier to read.
> 
> Nit: Why call thp_vma_suitable_orders if the orders are already 0?
> Again, some helper might be reasonable where that is handled internally.
> 
> Comment: For order-0 we'll always perform a function call to both
> thp_vma_allowable_orders() / thp_vma_suitable_orders(). We should
> perform some fast and efficient check if any <PMD THP are even enabled
> in the system / for this VMA, and in that case just fallback before
> doing more expensive checks.

Correction: only a call to thp_vma_allowable_orders(). I wonder if we 
can move some of thp_vma_allowable_orders() into the header file where 
we'd just check as fast and as efficiently for "no THP < PMD_THP 
enabled" on this system.

-- 
Cheers,

David / dhildenb