Re: [Xen-devel] [PATCHv6 3/3] xen/privcmd: improve performance of MMAPBATCH_V2

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 09/03/15 12:25, Stefano Stabellini wrote:
> On Fri, 6 Mar 2015, David Vrabel wrote:
>> 
>> +/*
>> + * Similar to traverse_pages, but use each page as a "block" of
>> + * data to be processed as one unit.
>> + */
>> +static int traverse_pages_block(unsigned nelem, size_t size,
>> +                            struct list_head *pos,
>> +                            int (*fn)(void *data, int nr, void *state),
>> +                            void *state)
>> +{
>> +    void *pagedata;
>> +    unsigned pageidx;
>> +    int ret = 0;
>> +
>> +    BUG_ON(size > PAGE_SIZE);
> 
> I looks like that PAGE_SIZE needs to be a multiple of size. Maybe we can
> add a BUG_ON for that too.

There is no such requirement because...

>> +    pageidx = PAGE_SIZE;
>> +
>> +    while (nelem) {
>> +            int nr = (PAGE_SIZE/size);

...the number of elements per pages is rounded down here.

>> +            struct page *page;
>> +            if (nr > nelem)
>> +                    nr = nelem;
>> +            pos = pos->next;
>> +            page = list_entry(pos, struct page, lru);
>> +            pagedata = page_address(page);
>> +            ret = (*fn)(pagedata, nr, state);
>> +            if (ret)
>> +                    break;
>> +            nelem -= nr;
>> +    }
>> +
>> +    return ret;
>> +}

David

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