[RFC PATCH 0/9] mm/zbud: support highmem pages

From: Heesub Shin
Date: Tue Oct 14 2014 - 07:59:57 EST

zbud is a memory allocator for storing compressed data pages. It keeps
two data objects of arbitrary size on a single page. This simple design
provides very deterministic behavior on reclamation, which is one of
reasons why zswap selected zbud as a default allocator over zsmalloc.

Unlike zsmalloc, however, zbud does not support highmem. This is
problomatic especially on 32-bit machines having relatively small
lowmem. Compressing anonymous pages from highmem and storing them into
lowmem could eat up lowmem spaces.

This limitation is due to the fact that zbud manages its internal data
structures on zbud_header which is kept in the head of zbud_page. For
example, zbud_pages are tracked by several lists and have some status
information, which are being referenced at any time by the kernel. Thus,
zbud_pages should be allocated on a memory region directly mapped,

After some digging out, I found that internal data structures of zbud
can be kept in the struct page, the same way as zsmalloc does. So, this
series moves out all fields in zbud_header to struct page. Though it
alters quite a lot, it does not add any functional differences except
highmem support. I am afraid that this kind of modification abusing
several fields in struct page would be ok.

Heesub Shin (9):
mm/zbud: tidy up a bit
mm/zbud: remove buddied list from zbud_pool
mm/zbud: remove lru from zbud_header
mm/zbud: remove first|last_chunks from zbud_header
mm/zbud: encode zbud handle using struct page
mm/zbud: remove list_head for buddied list from zbud_header
mm/zbud: drop zbud_header
mm/zbud: allow clients to use highmem pages
mm/zswap: use highmem pages for compressed pool

mm/zbud.c | 244 ++++++++++++++++++++++++++++++-------------------------------
mm/zswap.c | 4 +-
2 files changed, 121 insertions(+), 127 deletions(-)


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