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Message-ID: <10cdc414-c2d6-90c0-2810-9cdda0323423@arm.com>
Date:   Wed, 19 Jul 2023 19:46:46 +0100
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Subject: Re: [PATCH v2 2/3] mm: Implement folio_remove_rmap_range()
To:     Yu Zhao <yuzhao@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Matthew Wilcox <willy@infradead.org>,
        Yin Fengwei <fengwei.yin@intel.com>,
        David Hildenbrand <david@redhat.com>,
        Yang Shi <shy828301@gmail.com>,
        "Huang, Ying" <ying.huang@intel.com>, Zi Yan <ziy@nvidia.com>,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
References: <20230719135450.545227-1-ryan.roberts@arm.com>
 <20230719135450.545227-3-ryan.roberts@arm.com>
 <CAOUHufZrrPBkdEYWnGnbTTHxp8bveSOocPB3J=+nu-VfYFdKZA@mail.gmail.com>
From:   Ryan Roberts <ryan.roberts@arm.com>
In-Reply-To: <CAOUHufZrrPBkdEYWnGnbTTHxp8bveSOocPB3J=+nu-VfYFdKZA@mail.gmail.com>
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On 19/07/2023 19:23, Yu Zhao wrote:
> On Wed, Jul 19, 2023 at 7:55 AM Ryan Roberts <ryan.roberts@arm.com> wrote:
>>
>> Like page_remove_rmap() but batch-removes the rmap for a range of pages
>> belonging to a folio. This can provide a small speedup due to less
>> manipuation of the various counters. But more crucially, if removing the
>> rmap for all pages of a folio in a batch, there is no need to
>> (spuriously) add it to the deferred split list, which saves significant
>> cost when there is contention for the split queue lock.
>>
>> All contained pages are accounted using the order-0 folio (or base page)
>> scheme.
>>
>> Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
>> Reviewed-by: Zi Yan <ziy@nvidia.com>
>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> 
> I have asked for this before but let me be very clear this time: we
> need to generalize the existing functions rather than add more
> specialized functions. Otherwise it'd get even harder to maintain down
> the road.

Yeah fair enough, my fault; I wrote this before I had your feedback on the other
rmap function and overlooked it when refactoring this. I'll fix it and repost.

> 
> folio_remove_rmap_range() needs to replace page_remove_rmap(). IOW,
> page_remove_rmap() is just a wrapper around folio_remove_rmap_range().