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From: Andrew Morton <akpm@linux-foundation.org>
To: Song Liu <songliubraving@fb.com>
Cc: <linux-mm@kvack.org>, <matthew.wilcox@oracle.com>,
	<kirill.shutemov@linux.intel.com>, <kernel-team@fb.com>,
	<william.kucharski@oracle.com>, <chad.mynhier@oracle.com>,
	<mike.kravetz@oracle.com>
Subject: Re: [PATCH v2 0/3] Enable THP for text section of non-shmem files
Date: Tue, 18 Jun 2019 14:12:23 -0700
Message-ID: <20190618141223.4479989e18b1e1ea942b0e42@linux-foundation.org> (raw)
In-Reply-To: <20190614182204.2673660-1-songliubraving@fb.com>

On Fri, 14 Jun 2019 11:22:01 -0700 Song Liu <songliubraving@fb.com> wrote:

> This set follows up discussion at LSF/MM 2019. The motivation is to put
> text section of an application in THP, and thus reduces iTLB miss rate and
> improves performance. Both Facebook and Oracle showed strong interests to
> this feature.
> 
> To make reviews easier, this set aims a mininal valid product. Current
> version of the work does not have any changes to file system specific
> code. This comes with some limitations (discussed later).
> 
> This set enables an application to "hugify" its text section by simply
> running something like:
> 
>           madvise(0x600000, 0x80000, MADV_HUGEPAGE);
> 
> Before this call, the /proc/<pid>/maps looks like:
> 
>     00400000-074d0000 r-xp 00000000 00:27 2006927     app
> 
> After this call, part of the text section is split out and mapped to THP:
> 
>     00400000-00425000 r-xp 00000000 00:27 2006927     app
>     00600000-00e00000 r-xp 00200000 00:27 2006927     app   <<< on THP
>     00e00000-074d0000 r-xp 00a00000 00:27 2006927     app
> 
> Limitations:
> 
> 1. This only works for text section (vma with VM_DENYWRITE).
> 2. Once the application put its own pages in THP, the file is read only.
>    open(file, O_WRITE) will fail with -ETXTBSY. To modify/update the file,
>    it must be removed first.

Removed?  Even if the original mmap/madvise has gone away?  hm.

I'm wondering if this limitation can be abused in some fashion: mmap a
file to which you have read permissions, run madvise(MADV_HUGEPAGE) and
thus prevent the file's owner from being able to modify the file?  Or
something like that.  What are the issues and protections here?



  parent reply index

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-14 18:22 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
2019-06-18 21:12 ` Andrew Morton [this message]
2019-06-18 21:48   ` [PATCH v2 0/3] Enable THP for text section of non-shmem files 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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