Messages in this thread | | | Subject | Re: [PATCH -v2 1/2] mm, swap: Use kvzalloc to allocate some swap data structure | From | Dave Hansen <> | Date | Fri, 24 Mar 2017 06:56:10 -0700 |
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On 03/24/2017 12:33 AM, John Hubbard wrote: > There might be some additional information you are using to come up with > that conclusion, that is not obvious to me. Any thoughts there? These > calls use the same underlying page allocator (and I thought that both > were subject to the same constraints on defragmentation, as a result of > that). So I am not seeing any way that kmalloc could possibly be a > less-fragmenting call than vmalloc.
You guys are having quite a discussion over a very small point.
But, Ying is right.
Let's say we have a two-page data structure. vmalloc() takes two effectively random order-0 pages, probably from two different 2M pages and pins them. That "kills" two 2M pages.
kmalloc(), allocating two *contiguous* pages, is very unlikely to cross a 2M boundary (it theoretically could). That means it will only "kill" the possibility of a single 2M page. More 2M pages == less fragmentation.
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