Re: [PATCH] Add __GFP_MOVABLE for callers to flag allocations thatmay be migrated

From: Andrew Morton
Date: Thu Nov 30 2006 - 20:32:10 EST

On Thu, 30 Nov 2006 17:07:46 +0000
mel@xxxxxxxxx (Mel Gorman) wrote:

> Am reporting this patch after there were no further comments on the last
> version.

Am not sure what to do with it - nothing actually uses __GFP_MOVABLE.

> It is often known at allocation time when a page may be migrated or not.

"often", yes.

> This
> page adds a flag called __GFP_MOVABLE and GFP_HIGH_MOVABLE. Allocations using
> the __GFP_MOVABLE can be either migrated using the page migration mechanism
> or reclaimed by syncing with backing storage and discarding.
> Additional credit goes to Christoph Lameter and Linus Torvalds for shaping
> the concept. Credit to Hugh Dickens for catching issues with shmem swap
> vector and ramfs allocations.
> ...
> @@ -65,7 +65,7 @@ static inline void clear_user_highpage(s
> static inline struct page *
> alloc_zeroed_user_highpage(struct vm_area_struct *vma, unsigned long vaddr)
> {
> - struct page *page = alloc_page_vma(GFP_HIGHUSER, vma, vaddr);
> + struct page *page = alloc_page_vma(GFP_HIGH_MOVABLE, vma, vaddr);
> if (page)
> clear_user_highpage(page, vaddr);

But this change is presumptuous. alloc_zeroed_user_highpage() doesn't know
that its caller is going to use the page for moveable purposes. (Ditto lots
of other places in this patch).

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