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mm: submit multipage write for SWP_FS_OPS swap-space 

swap_writepage() is given one page at a time, but may be called repeatedly
in succession.

For block-device swapspace, the blk_plug functionality allows the multiple
pages to be combined together at lower layers.  That cannot be used for
SWP_FS_OPS as blk_plug may not exist - it is only active when
CONFIG_BLOCK=y.  Consequently all swap reads over NFS are single page
reads.

With this patch we pass a pointer-to-pointer via the wbc.  swap_writepage
can store state between calls - much like the pointer passed explicitly to
swap_readpage.  After calling swap_writepage() some number of times, the
state will be passed to swap_write_unplug() which can submit the combined
request.

Link: https://lkml.kernel.org/r/164859778128.29473.5191868522654408537.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: David Howells <dhowells@redhat.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
NeilBrown 2022-05-09 18:20:49 -07:00 committed by akpm
parent 5169b844b7
commit 2282679fb2
4 changed files with 74 additions and 24 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
include/linux/writeback.h
View File

@ -80,6 +80,13 @@ struct writeback_control {
unsigned punt_to_cgroup:1; /* cgrp punting, see __REQ_CGROUP_PUNT */
/* To enable batching of swap writes to non-block-device backends,
* "plug" can be set point to a 'struct swap_iocb *'. When all swap
* writes have been submitted, if with swap_iocb is not NULL,
* swap_write_unplug() should be called.
*/
struct swap_iocb **swap_plug;
#ifdef CONFIG_CGROUP_WRITEBACK
struct bdi_writeback *wb; /* wb this writeback is issued under */
struct inode *inode; /* inode being written out */

78
mm/page_io.c
View File

@ -259,8 +259,9 @@ static void sio_write_complete(struct kiocb *iocb, long ret)
{
struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);
struct page *page = sio->bvec[0].bv_page;
int p;
if (ret != PAGE_SIZE) {
if (ret != PAGE_SIZE * sio->pages) {
/*
* In the case of swap-over-nfs, this can be a
* temporary failure if the system has limited
@ -271,43 +272,63 @@ static void sio_write_complete(struct kiocb *iocb, long ret)
* the normal direct-to-bio case as it could
* be temporary.
*/
set_page_dirty(page);
ClearPageReclaim(page);
pr_err_ratelimited("Write error %ld on dio swapfile (%llu)\n",
ret, page_file_offset(page));
for (p = 0; p < sio->pages; p++) {
page = sio->bvec[p].bv_page;
set_page_dirty(page);
ClearPageReclaim(page);
}
} else
count_vm_event(PSWPOUT);
end_page_writeback(page);
count_vm_events(PSWPOUT, sio->pages);
for (p = 0; p < sio->pages; p++)
end_page_writeback(sio->bvec[p].bv_page);
mempool_free(sio, sio_pool);
}
static int swap_writepage_fs(struct page *page, struct writeback_control *wbc)
{
struct swap_iocb *sio;
struct swap_iocb *sio = NULL;
struct swap_info_struct *sis = page_swap_info(page);
struct file *swap_file = sis->swap_file;
struct address_space *mapping = swap_file->f_mapping;
struct iov_iter from;
int ret;
loff_t pos = page_file_offset(page);
set_page_writeback(page);
unlock_page(page);
sio = mempool_alloc(sio_pool, GFP_NOIO);
init_sync_kiocb(&sio->iocb, swap_file);
sio->iocb.ki_complete = sio_write_complete;
sio->iocb.ki_pos = page_file_offset(page);
sio->bvec[0].bv_page = page;
sio->bvec[0].bv_len = PAGE_SIZE;
sio->bvec[0].bv_offset = 0;
iov_iter_bvec(&from, WRITE, &sio->bvec[0], 1, PAGE_SIZE);
ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
if (ret != -EIOCBQUEUED)
sio_write_complete(&sio->iocb, ret);
return ret;
if (wbc->swap_plug)
sio = *wbc->swap_plug;
if (sio) {
if (sio->iocb.ki_filp != swap_file ||
sio->iocb.ki_pos + sio->pages * PAGE_SIZE != pos) {
swap_write_unplug(sio);
sio = NULL;
}
}
if (!sio) {
sio = mempool_alloc(sio_pool, GFP_NOIO);
init_sync_kiocb(&sio->iocb, swap_file);
sio->iocb.ki_complete = sio_write_complete;
sio->iocb.ki_pos = pos;
sio->pages = 0;
}
sio->bvec[sio->pages].bv_page = page;
sio->bvec[sio->pages].bv_len = PAGE_SIZE;
sio->bvec[sio->pages].bv_offset = 0;
sio->pages += 1;
if (sio->pages == ARRAY_SIZE(sio->bvec) || !wbc->swap_plug) {
swap_write_unplug(sio);
sio = NULL;
}
if (wbc->swap_plug)
*wbc->swap_plug = sio;
return 0;
}
int __swap_writepage(struct page *page, struct writeback_control *wbc,
bio_end_io_t end_write_func)
bio_end_io_t end_write_func)
{
struct bio *bio;
int ret;
@ -344,6 +365,19 @@ int __swap_writepage(struct page *page, struct writeback_control *wbc,
return 0;
}
void swap_write_unplug(struct swap_iocb *sio)
{
struct iov_iter from;
struct address_space *mapping = sio->iocb.ki_filp->f_mapping;
int ret;
iov_iter_bvec(&from, WRITE, sio->bvec, sio->pages,
PAGE_SIZE * sio->pages);
ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
if (ret != -EIOCBQUEUED)
sio_write_complete(&sio->iocb, ret);
}
static void sio_read_complete(struct kiocb *iocb, long ret)
{
struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);

4
mm/swap.h
View File

@ -16,6 +16,7 @@ static inline void swap_read_unplug(struct swap_iocb *plug)
if (unlikely(plug))
__swap_read_unplug(plug);
}
void swap_write_unplug(struct swap_iocb *sio);
int swap_writepage(struct page *page, struct writeback_control *wbc);
void end_swap_bio_write(struct bio *bio);
int __swap_writepage(struct page *page, struct writeback_control *wbc,
@ -71,6 +72,9 @@ static inline int swap_readpage(struct page *page, bool do_poll,
{
return 0;
}
static inline void swap_write_unplug(struct swap_iocb *sio)
{
}
static inline struct address_space *swap_address_space(swp_entry_t entry)
{

9
mm/vmscan.c
View File

@ -1156,7 +1156,8 @@ typedef enum {
* pageout is called by shrink_page_list() for each dirty page.
* Calls ->writepage().
*/
static pageout_t pageout(struct folio *folio, struct address_space *mapping)
static pageout_t pageout(struct folio *folio, struct address_space *mapping,
struct swap_iocb **plug)
{
/*
* If the folio is dirty, only perform writeback if that write
@ -1201,6 +1202,7 @@ static pageout_t pageout(struct folio *folio, struct address_space *mapping)
.range_start = 0,
.range_end = LLONG_MAX,
.for_reclaim = 1,
.swap_plug = plug,
};
folio_set_reclaim(folio);
@ -1533,6 +1535,7 @@ static unsigned int shrink_page_list(struct list_head *page_list,
unsigned int nr_reclaimed = 0;
unsigned int pgactivate = 0;
bool do_demote_pass;
struct swap_iocb *plug = NULL;
memset(stat, 0, sizeof(*stat));
cond_resched();
@ -1814,7 +1817,7 @@ retry:
* starts and then write it out here.
*/
try_to_unmap_flush_dirty();
switch (pageout(folio, mapping)) {
switch (pageout(folio, mapping, &plug)) {
case PAGE_KEEP:
goto keep_locked;
case PAGE_ACTIVATE:
@ -1968,6 +1971,8 @@ keep:
list_splice(&ret_pages, page_list);
count_vm_events(PGACTIVATE, pgactivate);
if (plug)
swap_write_unplug(plug);
return nr_reclaimed;
}