Re: [PATCH] mm: remove zap_page_range and create zap_vma_pages

From: Michal Hocko <mhocko@suse.com>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
	linux-s390@vger.kernel.org, netdev@vger.kernel.org,
	Christoph Hellwig <hch@infradead.org>,
	David Hildenbrand <david@redhat.com>,
	Peter Xu <peterx@redhat.com>, Nadav Amit <nadav.amit@gmail.com>,
	Matthew Wilcox <willy@infradead.org>,
	Vlastimil Babka <vbabka@suse.cz>, Rik van Riel <riel@surriel.com>,
	Will Deacon <will@kernel.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Christian Borntraeger <borntraeger@linux.ibm.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Christian Brauner <brauner@kernel.org>,
	Eric Dumazet <edumazet@google.com>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm: remove zap_page_range and create zap_vma_pages
Date: Wed, 4 Jan 2023 08:46:21 +0100	[thread overview]
Message-ID: <Y7UuzV94Yo59PwTa@dhcp22.suse.cz> (raw)
In-Reply-To: <20230104002732.232573-1-mike.kravetz@oracle.com>

On Tue 03-01-23 16:27:32, Mike Kravetz wrote:
> zap_page_range was originally designed to unmap pages within an address
> range that could span multiple vmas.  While working on [1], it was
> discovered that all callers of zap_page_range pass a range entirely within
> a single vma.  In addition, the mmu notification call within zap_page
> range does not correctly handle ranges that span multiple vmas.  When
> crossing a vma boundary, a new mmu_notifier_range_init/end call pair
> with the new vma should be made.
> 
> Instead of fixing zap_page_range, do the following:
> - Create a new routine zap_vma_pages() that will remove all pages within
>   the passed vma.  Most users of zap_page_range pass the entire vma and
>   can use this new routine.
> - For callers of zap_page_range not passing the entire vma, instead call
>   zap_page_range_single().
> - Remove zap_page_range.
> 
> [1] https://lore.kernel.org/linux-mm/20221114235507.294320-2-mike.kravetz@oracle.com/
> Suggested-by: Peter Xu <peterx@redhat.com>
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>

This looks even better than the previous version.
Acked-by: Michal Hocko <mhocko@suse.com>

minor nit

[...]
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index ad608ef2a243..ffa36cfe5884 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2713,7 +2713,7 @@ void folio_account_cleaned(struct folio *folio, struct bdi_writeback *wb)
>   *
>   * The caller must hold lock_page_memcg().  Most callers have the folio
>   * locked.  A few have the folio blocked from truncation through other
> - * means (eg zap_page_range() has it mapped and is holding the page table
> + * means (eg zap_vma_pages() has it mapped and is holding the page table
>   * lock).  This can also be called from mark_buffer_dirty(), which I
>   * cannot prove is always protected against truncate.

strictly speaking this should be unmap_page_range
-- 
Michal Hocko
SUSE Labs