> From: "Matthew Wilcox" <matthew@xxxxxx>
> To: "Alexandre Depoutovitch" <adepoutovitch@xxxxxxxxxx>
> Cc: linux-nfs@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx
> Sent: Monday, April 30, 2012 3:56:46 PM
> Subject: Re: [PATCH RFC v2] Performing direct I/O on sector-aligned requests
>
> On Sun, Apr 29, 2012 at 02:03:41PM -0700, Alexandre Depoutovitch
> wrote:
> > + if (current->mm) {
> > + ret = get_user_pages_fast(
> > + dio->curr_user_address, /* Where from? */
> > + nr_pages, /* How many pages? */
> > + dio->rw == READ, /* Write to memory? */
> > + &dio->pages[0]); /* Put results here */
> > + } else {
> > + /* For kernel threads mm is NULL, so all we need is to
> > increment
> > + page's reference count and add page to dio->pages array */
> > + int i;
> > + struct page* page;
> > + unsigned long start_pfn = virt_to_phys((void
> > *)dio->curr_user_address)
> > + >> PAGE_SHIFT;
> > + /* For kernel threads buffer must be in kernel memory */
> > + BUG_ON(dio->curr_user_address < TASK_SIZE_MAX);
>
> This is an assumption that isn't true for all architectures. Better
> just
> delete this line.
Thank you, I will do this.
> > + for (i = 0; i < nr_pages; i++) {
> > + page = pfn_to_page(start_pfn + i);
>
> Why are you messing about with pfns? Why not just stay with virtual
> addresses and call virt_to_page() in this loop? That would ensure
> that
> this works to vmapped pages as well as physically contiguous pages.
I have already changed this. Thanks.
> > + page_cache_get(page);
> > + dio->pages[i] = page;
> > + }
> > + /* No need to lock pages: this is kernel thread and the
> > pages are in
> > + kernel as well */
> > + ret = nr_pages;
> > + }
> >
> > if (ret < 0 && dio->blocks_available && (dio->rw & WRITE)) {
> > struct page *page = ZERO_PAGE(0);
> > @@ -972,7 +991,11 @@
> > break;
> > }
> >
> > - /* Drop the ref which was taken in get_user_pages() */
> > + /*
> > + * Drop the ref which was taken in dio_refill_pages
> > + * directly (for direct I/O) or by calling get_user_pages
> > + * (for buffered IO)
> > + */
>
> I think your change to this comment actually makes it more confusing.
I will remove it if is confusing.
> > @@ -1348,6 +1351,58 @@
> > nfsd_max_blksize);
> > }
> >
> > +int nfsd_directio_mode = DIO_NEVER;
> > +
> > +/**
> > + * nfsd_directio_mode - sets conditions when direct IO is
> > activated
> > + *
> > + * Input:
> > + * buf: ignored
> > + * size: zero
> > + *
> > + * OR
> > + *
> > + * Input:
> > + * buf: C string containing an unsigned
> > + * integer value representing the new
> > + * NFS direct IO mode
> > + * size: non-zero length of C string in @buf
> > + * Output:
> > + * On success: passed-in buffer filled with '\n'-terminated C
> > string
> > + * containing numeric value of the current direct IO mode
> > + * return code is the size in bytes of the string
> > + *
> > + * Possible modes are:
> > + * DIO_NEVER (0) - never use direct I/O
> > + * DIO_FS_UNALIGNED (1) - use direct I/O only for requests
> > that FS
> > unaligned
> > + * and block device aligned
> > + * DIO_SECTOR_ALIGNED (3) - use direct I/O for all block
> > device aligned
> > IO
> > + * On error: return code is zero or a negative errno value
> > + */
>
> This is not correct kerneldoc formatting.
I copy/pasted it from the previous entry in the same file :(
> --
> Matthew Wilcox Intel Open Source Technology Centre
> "Bill, look, we understand that you're interested in selling us this
> operating system, but compare it to ours. We can't possibly take
> such
> a retrograde step."
>
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