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From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Song Liu <songliubraving@fb.com>
Cc: Linux-MM <linux-mm@kvack.org>,
	Matthew Wilcox <matthew.wilcox@oracle.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	Kernel Team <Kernel-team@fb.com>,
	William Kucharski <william.kucharski@oracle.com>,
	Chad Mynhier <chad.mynhier@oracle.com>,
	Mike Kravetz <mike.kravetz@oracle.com>
Subject: Re: [PATCH v2 3/3] mm,thp: add read-only THP support for (non-shmem) FS
Date: Fri, 21 Jun 2019 16:11:33 +0300
Message-ID: <20190621131133.tafbzskbvquaaa7m@box> (raw)
In-Reply-To: <B83B2259-7CF5-411E-BC4C-7112657FC48E@fb.com>

On Fri, Jun 21, 2019 at 01:08:39PM +0000, Song Liu wrote:
> 
> Hi Kirill,
> 
> > On Jun 21, 2019, at 5:58 AM, Kirill A. Shutemov <kirill@shutemov.name> wrote:
> > 
> > On Fri, Jun 14, 2019 at 11:22:04AM -0700, Song Liu wrote:
> >> This patch is (hopefully) the first step to enable THP for non-shmem
> >> filesystems.
> >> 
> >> This patch enables an application to put part of its text sections to THP
> >> via madvise, for example:
> >> 
> >>    madvise((void *)0x600000, 0x200000, MADV_HUGEPAGE);
> >> 
> >> We tried to reuse the logic for THP on tmpfs. The following functions are
> >> renamed to reflect the new functionality:
> >> 
> >> 	collapse_shmem()	=>  collapse_file()
> >> 	khugepaged_scan_shmem()	=>  khugepaged_scan_file()
> >> 
> >> Currently, write is not supported for non-shmem THP. This is enforced by
> >> taking negative i_writecount. Therefore, if file has THP pages in the
> >> page cache, open() to write will fail. To update/modify the file, the
> >> user need to remove it first.
> >> 
> >> An EXPERIMENTAL config, READ_ONLY_THP_FOR_FS, is added to gate this
> >> feature.
> > 
> > Please document explicitly that the feature opens local DoS attack: any
> > user with read access to file can block write to the file by using
> > MADV_HUGEPAGE for a range of the file.
> > 
> > As is it only has to be used with trusted userspace.
> > 
> > We also might want to have mount option in addition to Kconfig option to
> > enable the feature on per-mount basis.
> 
> This behavior has been removed from v3 to v5. 

Yes, I've catch up with that. :P

-- 
 Kirill A. Shutemov


  reply index

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-14 18:22 [PATCH v2 0/3] Enable THP for text section of non-shmem files Song Liu
2019-06-14 18:22 ` [PATCH v2 1/3] mm: check compound_head(page)->mapping in filemap_fault() Song Liu
2019-06-17 14:59   ` Rik van Riel
2019-06-14 18:22 ` [PATCH v2 2/3] mm,thp: stats for file backed THP Song Liu
2019-06-17 15:00   ` Rik van Riel
2019-06-21 12:50   ` Kirill A. Shutemov
2019-06-21 14:09     ` Song Liu
2019-06-14 18:22 ` [PATCH v2 3/3] mm,thp: add read-only THP support for (non-shmem) FS Song Liu
2019-06-17 15:42   ` Rik van Riel
2019-06-21 12:58   ` Kirill A. Shutemov
2019-06-21 13:08     ` Song Liu
2019-06-21 13:11       ` Kirill A. Shutemov [this message]
2019-06-18 21:12 ` [PATCH v2 0/3] Enable THP for text section of non-shmem files Andrew Morton
2019-06-18 21:48   ` Song Liu
2019-06-20  1:13     ` Andrew Morton
2019-06-20  2:04       ` Song Liu
2019-06-19  6:26   ` Song Liu

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