From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Jan Beulich" <JBeulich@suse.com>
Subject: Re: [PATCH v5 1/4] xen: introduce a helper to allocate
 non-contiguous memory
Date: Fri, 08 May 2015 16:08:59 +0100
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To: Andrew Cooper <andrew.cooper3@citrix.com>, Roger Pau Monne <roger.pau@citrix.com>, xen-devel@lists.xenproject.org
Cc: Tim Deegan <tim@xen.org>, Stefano Stabellini <stefano.stabellini@citrix.com>, Ian Campbell <ian.campbell@citrix.com>
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>>> On 08.05.15 at 16:50, <andrew.cooper3@citrix.com> wrote:
> On 08/05/15 15:34, Roger Pau Monne wrote:
>> +
>> +void *vmalloc(unsigned long size)
>> +{
>> +    unsigned long *mfn;
>> +    unsigned long pages, i;
>> +    struct page_info *pg;
>> +    void *va = NULL;
>> +
>> +    ASSERT(!in_irq());
>> +
>> +    if ( size == 0 )
>> +        return ZERO_BLOCK_PTR;
>> +
>> +    pages = DIV_ROUND_UP(size, PAGE_SIZE);
>> +    mfn = xzalloc_array(unsigned long, pages);
> 
> This can avoid the zeroing if...
> 
>> +    if ( mfn == NULL )
>> +        return NULL;
>> +
>> +    for ( i = 0; i < pages; i++ )
>> +    {
>> +        pg = alloc_domheap_pages(NULL, 1, 0);
>> +        if ( pg == NULL )
>> +            goto error;
>> +        mfn[i] = page_to_mfn(pg);
>> +    }
>> +
>> +    va = vmap(mfn, pages);
>> +    if ( va == NULL )
>> +        goto error;
>> +
>> +    xfree(mfn);
>> +    return va;
>> +
>> + error:
>> +    vunmap(va);
>> +    for ( i = 0; i < pages; i++ )
>> +        if ( mfn[i] != 0 )
>> +            free_domheap_pages(mfn_to_page(mfn[i]), 1);
> 
> this loop turns into
> 
> while ( i )
>     free_domheap_pages(mfn_to_page(mfn[--i], 1);

or (preferably imo)

while ( i-- )
    free_domheap_pages(mfn_to_page(mfn[i], 1);

Jan