linux-kernel - Re: [PATCH] thp: fix data loss when splitting a file pmd

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Date:   Thu, 12 Jul 2018 16:42:10 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Ashwin Chaugule <ashwinch@...gle.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] thp: fix data loss when splitting a file pmd

On Thu, Jul 12, 2018 at 12:48:54AM +0000, Hugh Dickins wrote:
> __split_huge_pmd_locked() must check if the cleared huge pmd was dirty,
> and propagate that to PageDirty: otherwise, data may be lost when a huge
> tmpfs page is modified then split then reclaimed.
> 
> How has this taken so long to be noticed?  Because there was no problem
> when the huge page is written by a write system call (shmem_write_end()
> calls set_page_dirty()), nor when the page is allocated for a write fault
> (fault_dirty_shared_page() calls set_page_dirty()); but when allocated
> for a read fault (which MAP_POPULATE simulates), no set_page_dirty().

Yeah... Sorry.

Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

-- 
 Kirill A. Shutemov