On 03/15/2018 12:53 PM, Matthew Wilcox wrote: > From: Matthew Wilcox <mawil...@microsoft.com> > > Shrink page_frag_cache from 24 to 8 bytes (a single pointer to the > currently-in-use struct page) by using the page's refcount directly > (instead of maintaining a bias) and storing our current progress through > the page in the same bits currently used for page->index. We no longer > need to reflect the page pfmemalloc state if we're storing the page > directly. > > On the downside, we now call page_address() on every allocation, and we > do an atomic_inc() rather than a non-atomic decrement, but we should > touch the same number of cachelines and there is far less code (and > the code is less complex). > > Signed-off-by: Matthew Wilcox <mawil...@microsoft.com> > ---
One point about storing metadata not in struct page was to avoid false sharing. consumers of page frags call put_page() thus touching page refcount. With the pagecnt_bias (and other fields) we store in another cache line (private to the producer) we amortize the access to the shared cache line only when needed.
