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SubjectRe: [PATCH v2] page cache: Store only head pages in i_pages
On Fri, Feb 15, 2019 at 01:03:44AM +0300, Kirill A. Shutemov wrote:
> > + /*
> > + * A page got inserted in our range? Skip it. We have our
> > + * pages locked so they are protected from being removed.
> > + */
> > + if (page != pvec->pages[i]) {
>
> Maybe a comment for the VM_BUG while you're there?

Great idea. I didn't understand it the first time I looked at it either,
but I forgot to write a comment when I figured it out.

/*
* A page got inserted in our range? Skip it. We have our
* pages locked so they are protected from being removed.
+ * If we see a page whose index is higher than ours, it
+ * means our page has been removed, which shouldn't be
+ * possible because we're holding the PageLock.
*/
if (page != pvec->pages[i]) {

> > + /* Leave page->index set: truncation lookup relies on it */
> > +
> > + if (page->index + (1UL << compound_order(page)) - 1 ==
> > + xas.xa_index)
>
> It's 1am here and I'm slow, but it took me few minutes to understand how
> it works. Please add a comment.

I should get you to review at 1am more often! You're quite right.
Sleep-deprived Kirill spots problems that normal people would encounter.


/* Leave page->index set: truncation lookup relies on it */

+ /*
+ * Move to the next page in the vector if this is a small page
+ * or the index is of the last page in this compound page).
+ */
if (page->index + (1UL << compound_order(page)) - 1 ==
xas.xa_index)
i++;


Thanks for the review.

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