On Wed, Nov 04, 2020 at 04:30:05PM -0500, Kent Overstreet wrote:
> On Wed, Nov 04, 2020 at 08:42:03PM +0000, Matthew Wilcox (Oracle) wrote:
> > Increasing the batch size runs into diminishing returns. It's probably
> > better to make, eg, three calls to filemap_get_pages() than it is to
> > call into kmalloc().
>
> I have to disagree. Working with PAGEVEC_SIZE pages is eventually going to be
> like working with 4k pages today, and have you actually read the slub code for
> the kmalloc fast path? It's _really_ fast, there's no atomic operations and it
> doesn't even have to disable preemption - which is why you never see it showing
> up in profiles ever since we switched to slub.
>
> It would however be better to have a standard abstraction for this rather than
> open coding it - perhaps adding it to the pagevec code. Please don't just drop
> it, though.
I have the beginnings of a patch for that, but I got busy with other stuff
and didn't finish it.
diff --git a/include/linux/pagevec.h b/include/linux/pagevec.h
index 081d934eda64..b067d8aab874 100644
--- a/include/linux/pagevec.h
+++ b/include/linux/pagevec.h
@@ -18,13 +18,21 @@ struct page;
struct address_space;
struct pagevec {
- unsigned char nr;
- bool percpu_pvec_drained;
- struct page *pages[PAGEVEC_SIZE];
+ union {
+ struct {
+ unsigned char sz;
+ unsigned char nr;
+ bool percpu_pvec_drained;
+ struct page *pages[];
+ };
+ void *__p[PAGEVEC_SIZE + 1];
+ };
};
void __pagevec_release(struct pagevec *pvec);
void __pagevec_lru_add(struct pagevec *pvec);
+struct pagevec *pagevec_alloc(unsigned int sz, gfp_t gfp);
+void pagevec_free(struct pagevec *);
unsigned pagevec_lookup_entries(struct pagevec *pvec,
struct address_space *mapping,
pgoff_t start, unsigned nr_entries,
@@ -54,6 +62,7 @@ static inline unsigned pagevec_lookup_tag(struct pagevec *pvec,
static inline void pagevec_init(struct pagevec *pvec)
{
+ pvec->sz = PAGEVEC_SIZE;
pvec->nr = 0;
pvec->percpu_pvec_drained = false;
}
@@ -63,6 +72,11 @@ static inline void pagevec_reinit(struct pagevec *pvec)
pvec->nr = 0;
}
+static inline unsigned pagevec_size(struct pagevec *pvec)
+{
+ return pvec->sz;
+}
+
static inline unsigned pagevec_count(struct pagevec *pvec)
{
return pvec->nr;
