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Re: [PATCH] mm: add gfp_mask parameter to vm_map_ram()

To: Minchan Kim <minchan@xxxxxxxxxx>
Subject: Re: [PATCH] mm: add gfp_mask parameter to vm_map_ram()
From: Tejun Heo <tj@xxxxxxxxxx>
Date: Thu, 14 Jun 2012 11:21:32 +0900
Cc: Fengguang Wu <fengguang.wu@xxxxxxxxx>, Dave Chinner <dchinner@xxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>, linux-fsdevel@xxxxxxxxxxxxxxx, LKML <linux-kernel@xxxxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Linux Memory Management List <linux-mm@xxxxxxxxx>, xfs@xxxxxxxxxxx
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Sender: Tejun Heo <htejun@xxxxxxxxx>
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Hello, guys.

On Thu, Jun 14, 2012 at 11:07:53AM +0900, Minchan Kim wrote:
> It shouldn't work because vmap_page_range still can allocate
> GFP_KERNEL by pud_alloc in vmap_pud_range.  For it, I tried [1] but
> other mm guys want to add WARNING [2] so let's avoiding gfp context
> passing.
> [1] https://lkml.org/lkml/2012/4/23/77
> [2] https://lkml.org/lkml/2012/5/2/340

Yeah, vmalloc area doesn't support !GFP_KERNEL allocations and as
Minchan said, changing this would require updating page table
allocation functions on all archs.  This is the same reason why percpu
allocator doesn't support !GFP_KERNEL allocations which in turn made
blk-throttle implement its own private percpu pool.

If xfs can't live without GFP_NOFS vmalloc allocations, either it has
to implement its own pool or maybe it's time to implement !GFP_KERNEL
allocs for vmalloc area.  I don't know.



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