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mm/filemap: use head pages in generic_file_buffered_read

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Add filemap_get_read_batch() which returns the head pages which represent
a contiguous array of bytes in the file.  It also stops when encountering
a page marked as Readahead or !Uptodate (but does return that page) so it
can be handled appropriately by filemap_get_pages().  That lets us remove
the loop in filemap_get_pages() and check only the last page.

Link: https://lkml.kernel.org/r/20210122160140.223228-5-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Kent Overstreet <kent.overstreet@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Matthew Wilcox (Oracle) 2021-02-24 12:01:59 -08:00 committed by Linus Torvalds
parent ff993ba130
commit cbd59c48ae
1 changed files with 85 additions and 37 deletions
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122
mm/filemap.c
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@ -2178,6 +2178,51 @@ static int lock_page_for_iocb(struct kiocb *iocb, struct page *page)
return lock_page_killable(page);
}
/*
* filemap_get_read_batch - Get a batch of pages for read
*
* Get a batch of pages which represent a contiguous range of bytes
* in the file. No tail pages will be returned. If @index is in the
* middle of a THP, the entire THP will be returned. The last page in
* the batch may have Readahead set or be not Uptodate so that the
* caller can take the appropriate action.
*/
static void filemap_get_read_batch(struct address_space *mapping,
pgoff_t index, pgoff_t max, struct pagevec *pvec)
{
XA_STATE(xas, &mapping->i_pages, index);
struct page *head;
rcu_read_lock();
for (head = xas_load(&xas); head; head = xas_next(&xas)) {
if (xas_retry(&xas, head))
continue;
if (xas.xa_index > max || xa_is_value(head))
break;
if (!page_cache_get_speculative(head))
goto retry;
/* Has the page moved or been split? */
if (unlikely(head != xas_reload(&xas)))
goto put_page;
if (!pagevec_add(pvec, head))
break;
if (!PageUptodate(head))
break;
if (PageReadahead(head))
break;
xas.xa_index = head->index + thp_nr_pages(head) - 1;
xas.xa_offset = (xas.xa_index >> xas.xa_shift) & XA_CHUNK_MASK;
continue;
put_page:
put_page(head);
retry:
xas_reset(&xas);
}
rcu_read_unlock();
}
static struct page *filemap_read_page(struct kiocb *iocb, struct file *filp,
struct address_space *mapping, struct page *page)
{
@ -2331,15 +2376,15 @@ static int filemap_get_pages(struct kiocb *iocb, struct iov_iter *iter,
struct address_space *mapping = filp->f_mapping;
struct file_ra_state *ra = &filp->f_ra;
pgoff_t index = iocb->ki_pos >> PAGE_SHIFT;
pgoff_t last_index = (iocb->ki_pos + iter->count + PAGE_SIZE-1) >> PAGE_SHIFT;
unsigned int nr = min_t(unsigned long, last_index - index, PAGEVEC_SIZE);
int i, j, err = 0;
pgoff_t last_index;
int err = 0;
last_index = DIV_ROUND_UP(iocb->ki_pos + iter->count, PAGE_SIZE);
find_page:
if (fatal_signal_pending(current))
return -EINTR;
pvec->nr = find_get_pages_contig(mapping, index, nr, pvec->pages);
filemap_get_read_batch(mapping, index, last_index, pvec);
if (pvec->nr)
goto got_pages;
@ -2348,29 +2393,30 @@ find_page:
page_cache_sync_readahead(mapping, ra, filp, index, last_index - index);
pvec->nr = find_get_pages_contig(mapping, index, nr, pvec->pages);
filemap_get_read_batch(mapping, index, last_index, pvec);
if (pvec->nr)
goto got_pages;
pvec->pages[0] = filemap_create_page(iocb, iter);
err = PTR_ERR_OR_ZERO(pvec->pages[0]);
if (!IS_ERR_OR_NULL(pvec->pages[0]))
pvec->nr = 1;
if (IS_ERR_OR_NULL(pvec->pages[0]))
goto err;
pvec->nr = 1;
return 0;
got_pages:
for (i = 0; i < pvec->nr; i++) {
struct page *page = pvec->pages[i];
pgoff_t pg_index = index + i;
{
struct page *page = pvec->pages[pvec->nr - 1];
pgoff_t pg_index = page->index;
loff_t pg_pos = max(iocb->ki_pos,
(loff_t) pg_index << PAGE_SHIFT);
loff_t pg_count = iocb->ki_pos + iter->count - pg_pos;
if (PageReadahead(page)) {
if (iocb->ki_flags & IOCB_NOIO) {
for (j = i; j < pvec->nr; j++)
put_page(pvec->pages[j]);
pvec->nr = i;
put_page(page);
pvec->nr--;
err = -EAGAIN;
break;
goto err;
}
page_cache_async_readahead(mapping, ra, filp, page,
pg_index, last_index - pg_index);
@ -2378,26 +2424,23 @@ got_pages:
if (!PageUptodate(page)) {
if ((iocb->ki_flags & IOCB_NOWAIT) ||
((iocb->ki_flags & IOCB_WAITQ) && i)) {
for (j = i; j < pvec->nr; j++)
put_page(pvec->pages[j]);
pvec->nr = i;
((iocb->ki_flags & IOCB_WAITQ) && pvec->nr > 1)) {
put_page(page);
pvec->nr--;
err = -EAGAIN;
break;
goto err;
}
page = filemap_update_page(iocb, filp, iter, page,
pg_pos, pg_count);
if (IS_ERR_OR_NULL(page)) {
for (j = i + 1; j < pvec->nr; j++)
put_page(pvec->pages[j]);
pvec->nr = i;
pvec->nr--;
err = PTR_ERR_OR_ZERO(page);
break;
}
}
}
err:
if (likely(pvec->nr))
return 0;
if (err)
@ -2442,6 +2485,7 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
return 0;
iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
pagevec_init(&pvec);
do {
cond_resched();
@ -2469,13 +2513,8 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
isize = i_size_read(inode);
if (unlikely(iocb->ki_pos >= isize))
goto put_pages;
end_offset = min_t(loff_t, isize, iocb->ki_pos + iter->count);
while ((iocb->ki_pos >> PAGE_SHIFT) + pvec.nr >
(end_offset + PAGE_SIZE - 1) >> PAGE_SHIFT)
put_page(pvec.pages[--pvec.nr]);
/*
* Once we start copying data, we don't want to be touching any
* cachelines that might be contended:
@ -2489,24 +2528,32 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
if (iocb->ki_pos >> PAGE_SHIFT !=
ra->prev_pos >> PAGE_SHIFT)
mark_page_accessed(pvec.pages[0]);
for (i = 1; i < pagevec_count(&pvec); i++)
mark_page_accessed(pvec.pages[i]);
for (i = 0; i < pagevec_count(&pvec); i++) {
unsigned int offset = iocb->ki_pos & ~PAGE_MASK;
unsigned int bytes = min_t(loff_t, end_offset - iocb->ki_pos,
PAGE_SIZE - offset);
unsigned int copied;
struct page *page = pvec.pages[i];
size_t page_size = thp_size(page);
size_t offset = iocb->ki_pos & (page_size - 1);
size_t bytes = min_t(loff_t, end_offset - iocb->ki_pos,
page_size - offset);
size_t copied;
if (end_offset < page_offset(page))
break;
if (i > 0)
mark_page_accessed(page);
/*
* If users can be writing to this page using arbitrary
* virtual addresses, take care about potential aliasing
* before reading the page on the kernel side.
*/
if (writably_mapped)
flush_dcache_page(pvec.pages[i]);
if (writably_mapped) {
int j;
copied = copy_page_to_iter(pvec.pages[i], offset, bytes, iter);
for (j = 0; j < thp_nr_pages(page); j++)
flush_dcache_page(page + j);
}
copied = copy_page_to_iter(page, offset, bytes, iter);
written += copied;
iocb->ki_pos += copied;
@ -2520,6 +2567,7 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb,
put_pages:
for (i = 0; i < pagevec_count(&pvec); i++)
put_page(pvec.pages[i]);
pagevec_reinit(&pvec);
} while (iov_iter_count(iter) && iocb->ki_pos < isize && !error);
file_accessed(filp);