On 06/09/2012 04:29 AM, Konrad Rzeszutek Wilk wrote: > On Sun, Jun 03, 2012 at 01:20:05PM -0700, Nitin Gupta wrote: >> Signed-off-by: Nitin Gupta <ngupta@xxxxxxxxxx> >> --- >> drivers/staging/zsmalloc/zsmalloc-main.c | 49 ++++++++++++++++++++++++++++++ >> 1 file changed, 49 insertions(+) >> >> diff --git a/drivers/staging/zsmalloc/zsmalloc-main.c b/drivers/staging/zsmalloc/zsmalloc-main.c >> index 4496737..f80f2fd 100644 >> --- a/drivers/staging/zsmalloc/zsmalloc-main.c >> +++ b/drivers/staging/zsmalloc/zsmalloc-main.c >> @@ -10,6 +10,55 @@ >> * Released under the terms of GNU General Public License Version 2.0 >> */ >> >> + >> +/* >> + * This allocator is designed for use with zcache and zram. Thus, the >> + * allocator is supposed to work well under low memory conditions. In >> + * particular, it never attempts higher order page allocation which is >> + * very likely to fail under memory pressure. On the other hand, if we >> + * just use single (0-order) pages, it would suffer from very high >> + * fragmentation -- any object of size PAGE_SIZE/2 or larger would occupy >> + * an entire page. This was one of the major issues with its predecessor >> + * (xvmalloc). >> + * >> + * To overcome these issues, zsmalloc allocates a bunch of 0-order pages >> + * and links them together using various 'struct page' fields. These linked >> + * pages act as a single higher-order page i.e. an object can span 0-order >> + * page boundaries. The code refers to these linked pages as a single entity >> + * called zspage. >> + * >> + * Following is how we use various fields and flags of underlying >> + * struct page(s) to form a zspage. >> + * >> + * Usage of struct page fields: > > I took your definition and grouped them a bit differently: > Not sure if it is more easier to read? > > page->first_page: points to the first component (0-order) page > page->index (union with page->freelist): offset of the first object > starting in this page. For the first page, this is > always 0, so we use this field (aka freelist) to point > to the first free object in zspage. > page->lru: links together all component pages (except the first page) > of a zspage > > For _first_ page only: > > page->private (union with page->first_page): refers to the > component page after the first page > page->freelist: points to the first free object in zspage. > Free objects are linked together using in-place > metadata. > page->objects: maximum number of objects we can store in this > zspage (class->zspage_order * PAGE_SIZE / class->size) > page->lru: links together first pages of various zspages. > Basically forming list of zspages in a fullness group. > page->mapping: class index and fullness group of the zspage This regrouping indeed looks cleaner. I will send the revised patch soon. Thanks, Nitin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>