Re: Fine granularity page reclaim

[Ying Han <yinghan@google.com>]

On Fri, Feb 17, 2012 at 1:22 AM, Zheng Liu <gnehzuil.liu@gmail.com> wrote:
> Hi all,
>
> Currently, we encounter a problem about page reclaim. In our product system,
> there is a lot of applictions that manipulate a number of files. In these
> files, they can be divided into two categories. One is index file, another is
> block file. The number of index files is about 15,000, and the number of
> block files is about 23,000 in a 2TB disk. The application accesses index
> file using mmap(2), and read/write block file using pread(2)/pwrite(2). We hope
> to hold index file in memory as much as possible, and it works well in Redhat
> 2.6.18-164. It is about 60-70% of index files that can be hold in memory.
> However, it doesn't work well in Redhat 2.6.32-133. I know in 2.6.18 that the
> linux uses an active list and an inactive list to handle page reclaim, and in
> 2.6.32 that they are divided into anonymous list and file list. So I am
> curious about why most of index files can be hold in 2.6.18?

One of changes after the split-lru is different scan ratio (active vs
inactive) for file-lru and anon-lru. You can check the following two
functions:

inactive_anon_is_low_global()
inactive_file_is_low_global()

Depends on your machine size, we might end of scanning more pages on file lru.

--Ying

The index file
> should be replaced because mmap doesn't impact the lru list.
>
> BTW, I have some problems that need to be discussed.
>
> 1. I want to let index and block files are separately reclaimed. Is there any
> ways to satisify me in current upstream?
>
> 2. Maybe we can provide a mechansim to let different files to be mapped into
> differnet nodes. we can provide a ioctl(2) to tell kernel that this file should
> be mapped into a specific node id. A nid member is added into addpress_space
> struct. When alloc_page is called, the page can be allocated from that specific
> node id.
>
> 3. Currently the page can be reclaimed according to pid in memcg. But it is too
> coarse. I don't know whether memcg could provide a fine granularity page
> reclaim mechansim. For example, the page is reclaimed according to inode number.
>
> I don't subscribe this mailing list, So please Cc me. Thank you.
>
> Regards,
> Zheng
>
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