Re: [PATCH v5 2/5] allow mapping page-less memremaped areas into KVA
From: Boaz Harrosh
Date: Thu Aug 13 2015 - 10:49:27 EST
On 08/13/2015 05:37 PM, Christoph Hellwig wrote:
> Hi Boaz,
> can you please fix your quoting? I read down about 10 pages but still
> couldn't find a comment from you. For now I gave up on this mail.
> +void *kmap_atomic_pfn_t(__pfn_t pfn)
> + struct page *page = __pfn_t_to_page(pfn);
> + resource_size_t addr;
> + struct kmap *kmap;
> + rcu_read_lock();
> + if (page)
> + return kmap_atomic(page);
Right even with pages I pay rcu_read_lock(); for every access?
> + addr = __pfn_t_to_phys(pfn);
> + list_for_each_entry_rcu(kmap, &ranges, list)
> + if (addr >= kmap->res->start && addr <= kmap->res->end)
> + return kmap->base + addr - kmap->res->start;
Good god! This loop is a real *joke*. You have just dropped memory access
performance by 10 fold.
The all point of pages and memory_model.h was to have a one to one
relation-ships between Kernel-virtual vs physical vs page *
There is already an object that holds a relationship of physical
to Kernel-virtual. It is called a memory-section. Why not just
widen its definition?
If you are willing to accept this loop. In current Linux 2015 Kernel
Then I have nothing farther to say.
Boaz - go mourning for the death of the Linux Kernel alone in the corner ;-(
> + /* only unlock in the error case */
> + rcu_read_unlock();
> + return NULL;
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