Re: [PATCH 01/20] mm: mmu_gather rework

[Andrew Morton]

On Fri, 01 Apr 2011 14:12:59 +0200
Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:

> Remove the first obstackle towards a fully preemptible mmu_gather.
> 
> The current scheme assumes mmu_gather is always done with preemption
> disabled and uses per-cpu storage for the page batches. Change this to
> try and allocate a page for batching and in case of failure, use a
> small on-stack array to make some progress.
> 
> Preemptible mmu_gather is desired in general and usable once
> i_mmap_lock becomes a mutex. Doing it before the mutex conversion
> saves us from having to rework the code by moving the mmu_gather
> bits inside the pte_lock.
> 
> Also avoid flushing the tlb batches from under the pte lock,
> this is useful even without the i_mmap_lock conversion as it
> significantly reduces pte lock hold times.

There doesn't seem much point in reviewing this closely, as a lot of it
gets tossed away later in the series..

>  		free_pages_and_swap_cache(tlb->pages, tlb->nr);

It seems inappropriate that this code uses
free_page[s]_and_swap_cache().  It should go direct to put_page() and
release_pages()?  Please review this code's implicit decision to pass
"cold==0" into release_pages().

> -static inline void tlb_remove_page(struct mmu_gather *tlb, struct page *page)
> +static inline int __tlb_remove_page(struct mmu_gather *tlb, struct page *page)

I wonder if all the inlining which remains in this code is needed and
desirable.

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