Hi Hugh,
On 01/29/2013 01:03 PM, Hugh Dickins wrote:
> On Mon, 28 Jan 2013, Kirill A. Shutemov wrote:
>> From: "Kirill A. Shutemov" <[email protected]>
>>
>> Here's first steps towards huge pages in page cache.
>>
>> The intend of the work is get code ready to enable transparent huge page
>> cache for the most simple fs -- ramfs.
>>
>> It's not yet near feature-complete. It only provides basic infrastructure.
>> At the moment we can read, write and truncate file on ramfs with huge pages in
>> page cache. The most interesting part, mmap(), is not yet there. For now
>> we split huge page on mmap() attempt.
>>
>> I can't say that I see whole picture. I'm not sure if I understand locking
>> model around split_huge_page(). Probably, not.
>> Andrea, could you check if it looks correct?
>>
>> Next steps (not necessary in this order):
>> - mmap();
>> - migration (?);
>> - collapse;
>> - stats, knobs, etc.;
>> - tmpfs/shmem enabling;
>> - ...
>>
>> Kirill A. Shutemov (16):
>> block: implement add_bdi_stat()
>> mm: implement zero_huge_user_segment and friends
>> mm: drop actor argument of do_generic_file_read()
>> radix-tree: implement preload for multiple contiguous elements
>> thp, mm: basic defines for transparent huge page cache
>> thp, mm: rewrite add_to_page_cache_locked() to support huge pages
>> thp, mm: rewrite delete_from_page_cache() to support huge pages
>> thp, mm: locking tail page is a bug
>> thp, mm: handle tail pages in page_cache_get_speculative()
>> thp, mm: implement grab_cache_huge_page_write_begin()
>> thp, mm: naive support of thp in generic read/write routines
>> thp, libfs: initial support of thp in
>> simple_read/write_begin/write_end
>> thp: handle file pages in split_huge_page()
>> thp, mm: truncate support for transparent huge page cache
>> thp, mm: split huge page on mmap file page
>> ramfs: enable transparent huge page cache
>>
>> fs/libfs.c | 54 +++++++++---
>> fs/ramfs/inode.c | 6 +-
>> include/linux/backing-dev.h | 10 +++
>> include/linux/huge_mm.h | 8 ++
>> include/linux/mm.h | 15 ++++
>> include/linux/pagemap.h | 14 ++-
>> include/linux/radix-tree.h | 3 +
>> lib/radix-tree.c | 32 +++++--
>> mm/filemap.c | 204 +++++++++++++++++++++++++++++++++++--------
>> mm/huge_memory.c | 62 +++++++++++--
>> mm/memory.c | 22 +++++
>> mm/truncate.c | 12 +++
>> 12 files changed, 375 insertions(+), 67 deletions(-)
> Interesting.
>
> I was starting to think about Transparent Huge Pagecache a few
> months ago, but then got washed away by incoming waves as usual.
>
> Certainly I don't have a line of code to show for it; but my first
> impression of your patches is that we have very different ideas of
> where to start.
>
> Perhaps that's good complementarity, or perhaps I'll disagree with
> your approach. I'll be taking a look at yours in the coming days,
> and trying to summon back up my own ideas to summarize them for you.
>
> Perhaps I was naive to imagine it, but I did intend to start out
> generically, independent of filesystem; but content to narrow down
> on tmpfs alone where it gets hard to support the others (writeback
> springs to mind). khugepaged would be migrating little pages into
> huge pages, where it saw that the mmaps of the file would benefit
> (and for testing I would hack mmap alignment choice to favour it).
>
> I had arrived at a conviction that the first thing to change was
> the way that tail pages of a THP are refcounted, that it had been a
> mistake to use the compound page method of holding the THP together.
> But I'll have to enter a trance now to recall the arguments ;)
One offline question, do you have any idea hugetlbfs pages support swapping?
>
> Hugh
>
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