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mm: page cache: store only head pages in i_pages
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Transparent Huge Pages are currently stored in i_pages as pointers to
consecutive subpages.  This patch changes that to storing consecutive
pointers to the head page in preparation for storing huge pages more
efficiently in i_pages.

Large parts of this are "inspired" by Kirill's patch
https://lore.kernel.org/lkml/20170126115819.58875-2-kirill.shutemov@linux.intel.com/

Kirill and Huang Ying contributed several fixes.

[willy@infradead.org: use compound_nr, squish uninit-var warning]
Link: http://lkml.kernel.org/r/20190731210400.7419-1-willy@infradead.org
Signed-off-by: Matthew Wilcox <willy@infradead.org>
Acked-by: Jan Kara <jack@suse.cz>
Reviewed-by: Kirill Shutemov <kirill@shutemov.name>
Reviewed-by: Song Liu <songliubraving@fb.com>
Tested-by: Song Liu <songliubraving@fb.com>
Tested-by: William Kucharski <william.kucharski@oracle.com>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Tested-by: Qian Cai <cai@lca.pw>
Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Song Liu <songliubraving@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Matthew Wilcox (Oracle) authored and torvalds committed Sep 24, 2019
1 parent 875d91b commit 4101196
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Showing 8 changed files with 95 additions and 96 deletions.
10 changes: 10 additions & 0 deletions include/linux/pagemap.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -333,6 +333,16 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping,
mapping_gfp_mask(mapping));
}

static inline struct page *find_subpage(struct page *page, pgoff_t offset)
{
if (PageHuge(page))
return page;

VM_BUG_ON_PAGE(PageTail(page), page);

return page + (offset & (compound_nr(page) - 1));
}

struct page *find_get_entry(struct address_space *mapping, pgoff_t offset);
struct page *find_lock_entry(struct address_space *mapping, pgoff_t offset);
unsigned find_get_entries(struct address_space *mapping, pgoff_t start,
Expand Down
145 changes: 57 additions & 88 deletions mm/filemap.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -281,11 +281,11 @@ EXPORT_SYMBOL(delete_from_page_cache);
* @pvec: pagevec with pages to delete
*
* The function walks over mapping->i_pages and removes pages passed in @pvec
* from the mapping. The function expects @pvec to be sorted by page index.
* from the mapping. The function expects @pvec to be sorted by page index
* and is optimised for it to be dense.
* It tolerates holes in @pvec (mapping entries at those indices are not
* modified). The function expects only THP head pages to be present in the
* @pvec and takes care to delete all corresponding tail pages from the
* mapping as well.
* @pvec.
*
* The function expects the i_pages lock to be held.
*/
Expand All @@ -294,40 +294,43 @@ static void page_cache_delete_batch(struct address_space *mapping,
{
XA_STATE(xas, &mapping->i_pages, pvec->pages[0]->index);
int total_pages = 0;
int i = 0, tail_pages = 0;
int i = 0;
struct page *page;

mapping_set_update(&xas, mapping);
xas_for_each(&xas, page, ULONG_MAX) {
if (i >= pagevec_count(pvec) && !tail_pages)
if (i >= pagevec_count(pvec))
break;

/* A swap/dax/shadow entry got inserted? Skip it. */
if (xa_is_value(page))
continue;
if (!tail_pages) {
/*
* Some 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]) {
VM_BUG_ON_PAGE(page->index >
pvec->pages[i]->index, page);
continue;
}
WARN_ON_ONCE(!PageLocked(page));
if (PageTransHuge(page) && !PageHuge(page))
tail_pages = HPAGE_PMD_NR - 1;
/*
* 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]) {
VM_BUG_ON_PAGE(page->index > pvec->pages[i]->index,
page);
continue;
}

WARN_ON_ONCE(!PageLocked(page));

if (page->index == xas.xa_index)
page->mapping = NULL;
/*
* Leave page->index set: truncation lookup relies
* upon it
*/
/* Leave page->index set: truncation lookup relies on it */

/*
* Move to the next page in the vector if this is a regular
* page or the index is of the last sub-page of this compound
* page.
*/
if (page->index + compound_nr(page) - 1 == xas.xa_index)
i++;
} else {
VM_BUG_ON_PAGE(page->index + HPAGE_PMD_NR - tail_pages
!= pvec->pages[i]->index, page);
tail_pages--;
}
xas_store(&xas, NULL);
total_pages++;
}
Expand Down Expand Up @@ -1520,7 +1523,7 @@ EXPORT_SYMBOL(page_cache_prev_miss);
struct page *find_get_entry(struct address_space *mapping, pgoff_t offset)
{
XA_STATE(xas, &mapping->i_pages, offset);
struct page *head, *page;
struct page *page;

rcu_read_lock();
repeat:
Expand All @@ -1535,25 +1538,19 @@ struct page *find_get_entry(struct address_space *mapping, pgoff_t offset)
if (!page || xa_is_value(page))
goto out;

head = compound_head(page);
if (!page_cache_get_speculative(head))
goto repeat;

/* The page was split under us? */
if (compound_head(page) != head) {
put_page(head);
if (!page_cache_get_speculative(page))
goto repeat;
}

/*
* Has the page moved?
* Has the page moved or been split?
* This is part of the lockless pagecache protocol. See
* include/linux/pagemap.h for details.
*/
if (unlikely(page != xas_reload(&xas))) {
put_page(head);
put_page(page);
goto repeat;
}
page = find_subpage(page, offset);
out:
rcu_read_unlock();

Expand Down Expand Up @@ -1735,7 +1732,6 @@ unsigned find_get_entries(struct address_space *mapping,

rcu_read_lock();
xas_for_each(&xas, page, ULONG_MAX) {
struct page *head;
if (xas_retry(&xas, page))
continue;
/*
Expand All @@ -1746,17 +1742,13 @@ unsigned find_get_entries(struct address_space *mapping,
if (xa_is_value(page))
goto export;

head = compound_head(page);
if (!page_cache_get_speculative(head))
if (!page_cache_get_speculative(page))
goto retry;

/* The page was split under us? */
if (compound_head(page) != head)
goto put_page;

/* Has the page moved? */
/* Has the page moved or been split? */
if (unlikely(page != xas_reload(&xas)))
goto put_page;
page = find_subpage(page, xas.xa_index);

export:
indices[ret] = xas.xa_index;
Expand All @@ -1765,7 +1757,7 @@ unsigned find_get_entries(struct address_space *mapping,
break;
continue;
put_page:
put_page(head);
put_page(page);
retry:
xas_reset(&xas);
}
Expand Down Expand Up @@ -1807,33 +1799,27 @@ unsigned find_get_pages_range(struct address_space *mapping, pgoff_t *start,

rcu_read_lock();
xas_for_each(&xas, page, end) {
struct page *head;
if (xas_retry(&xas, page))
continue;
/* Skip over shadow, swap and DAX entries */
if (xa_is_value(page))
continue;

head = compound_head(page);
if (!page_cache_get_speculative(head))
if (!page_cache_get_speculative(page))
goto retry;

/* The page was split under us? */
if (compound_head(page) != head)
goto put_page;

/* Has the page moved? */
/* Has the page moved or been split? */
if (unlikely(page != xas_reload(&xas)))
goto put_page;

pages[ret] = page;
pages[ret] = find_subpage(page, xas.xa_index);
if (++ret == nr_pages) {
*start = xas.xa_index + 1;
goto out;
}
continue;
put_page:
put_page(head);
put_page(page);
retry:
xas_reset(&xas);
}
Expand Down Expand Up @@ -1878,7 +1864,6 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,

rcu_read_lock();
for (page = xas_load(&xas); page; page = xas_next(&xas)) {
struct page *head;
if (xas_retry(&xas, page))
continue;
/*
Expand All @@ -1888,24 +1873,19 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t index,
if (xa_is_value(page))
break;

head = compound_head(page);
if (!page_cache_get_speculative(head))
if (!page_cache_get_speculative(page))
goto retry;

/* The page was split under us? */
if (compound_head(page) != head)
goto put_page;

/* Has the page moved? */
/* Has the page moved or been split? */
if (unlikely(page != xas_reload(&xas)))
goto put_page;

pages[ret] = page;
pages[ret] = find_subpage(page, xas.xa_index);
if (++ret == nr_pages)
break;
continue;
put_page:
put_page(head);
put_page(page);
retry:
xas_reset(&xas);
}
Expand Down Expand Up @@ -1941,7 +1921,6 @@ unsigned find_get_pages_range_tag(struct address_space *mapping, pgoff_t *index,

rcu_read_lock();
xas_for_each_marked(&xas, page, end, tag) {
struct page *head;
if (xas_retry(&xas, page))
continue;
/*
Expand All @@ -1952,26 +1931,21 @@ unsigned find_get_pages_range_tag(struct address_space *mapping, pgoff_t *index,
if (xa_is_value(page))
continue;

head = compound_head(page);
if (!page_cache_get_speculative(head))
if (!page_cache_get_speculative(page))
goto retry;

/* The page was split under us? */
if (compound_head(page) != head)
goto put_page;

/* Has the page moved? */
/* Has the page moved or been split? */
if (unlikely(page != xas_reload(&xas)))
goto put_page;

pages[ret] = page;
pages[ret] = find_subpage(page, xas.xa_index);
if (++ret == nr_pages) {
*index = xas.xa_index + 1;
goto out;
}
continue;
put_page:
put_page(head);
put_page(page);
retry:
xas_reset(&xas);
}
Expand Down Expand Up @@ -2652,7 +2626,7 @@ void filemap_map_pages(struct vm_fault *vmf,
pgoff_t last_pgoff = start_pgoff;
unsigned long max_idx;
XA_STATE(xas, &mapping->i_pages, start_pgoff);
struct page *head, *page;
struct page *page;

rcu_read_lock();
xas_for_each(&xas, page, end_pgoff) {
Expand All @@ -2661,24 +2635,19 @@ void filemap_map_pages(struct vm_fault *vmf,
if (xa_is_value(page))
goto next;

head = compound_head(page);

/*
* Check for a locked page first, as a speculative
* reference may adversely influence page migration.
*/
if (PageLocked(head))
if (PageLocked(page))
goto next;
if (!page_cache_get_speculative(head))
if (!page_cache_get_speculative(page))
goto next;

/* The page was split under us? */
if (compound_head(page) != head)
goto skip;

/* Has the page moved? */
/* Has the page moved or been split? */
if (unlikely(page != xas_reload(&xas)))
goto skip;
page = find_subpage(page, xas.xa_index);

if (!PageUptodate(page) ||
PageReadahead(page) ||
Expand Down
22 changes: 20 additions & 2 deletions mm/huge_memory.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2497,13 +2497,23 @@ static void __split_huge_page(struct page *page, struct list_head *list,
struct page *head = compound_head(page);
pg_data_t *pgdat = page_pgdat(head);
struct lruvec *lruvec;
struct address_space *swap_cache = NULL;
unsigned long offset = 0;
int i;

lruvec = mem_cgroup_page_lruvec(head, pgdat);

/* complete memcg works before add pages to LRU */
mem_cgroup_split_huge_fixup(head);

if (PageAnon(head) && PageSwapCache(head)) {
swp_entry_t entry = { .val = page_private(head) };

offset = swp_offset(entry);
swap_cache = swap_address_space(entry);
xa_lock(&swap_cache->i_pages);
}

for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
__split_huge_page_tail(head, i, lruvec, list);
/* Some pages can be beyond i_size: drop them from page cache */
Expand All @@ -2513,6 +2523,12 @@ static void __split_huge_page(struct page *page, struct list_head *list,
if (IS_ENABLED(CONFIG_SHMEM) && PageSwapBacked(head))
shmem_uncharge(head->mapping->host, 1);
put_page(head + i);
} else if (!PageAnon(page)) {
__xa_store(&head->mapping->i_pages, head[i].index,
head + i, 0);
} else if (swap_cache) {
__xa_store(&swap_cache->i_pages, offset + i,
head + i, 0);
}
}

Expand All @@ -2523,10 +2539,12 @@ static void __split_huge_page(struct page *page, struct list_head *list,
/* See comment in __split_huge_page_tail() */
if (PageAnon(head)) {
/* Additional pin to swap cache */
if (PageSwapCache(head))
if (PageSwapCache(head)) {
page_ref_add(head, 2);
else
xa_unlock(&swap_cache->i_pages);
} else {
page_ref_inc(head);
}
} else {
/* Additional pin to page cache */
page_ref_add(head, 2);
Expand Down
4 changes: 2 additions & 2 deletions mm/khugepaged.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1378,7 +1378,7 @@ static void collapse_shmem(struct mm_struct *mm,
result = SCAN_FAIL;
goto xa_locked;
}
xas_store(&xas, new_page + (index % HPAGE_PMD_NR));
xas_store(&xas, new_page);
nr_none++;
continue;
}
Expand Down Expand Up @@ -1454,7 +1454,7 @@ static void collapse_shmem(struct mm_struct *mm,
list_add_tail(&page->lru, &pagelist);

/* Finally, replace with the new page. */
xas_store(&xas, new_page + (index % HPAGE_PMD_NR));
xas_store(&xas, new_page);
continue;
out_unlock:
unlock_page(page);
Expand Down
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