mm/fs: delete PF_SWAPWRITE

PF_SWAPWRITE has been redundant since v3.2 commit ee72886d ("mm:
vmscan: do not writeback filesystem pages in direct reclaim").

Coincidentally, NeilBrown's current patch "remove inode_congested()"
deletes may_write_to_inode(), which appeared to be the one function which
took notice of PF_SWAPWRITE.  But if you study the old logic, and the
conditions under which may_write_to_inode() was called, you discover that
flag and function have been pointless for a decade.

Link: https://lkml.kernel.org/r/75e80e7-742d-e3bd-531-614db8961e4@google.comSigned-off-by: Hugh Dickins <hughd@google.com>
Cc: NeilBrown <neilb@suse.de>
Cc: Jan Kara <jack@suse.de>
Cc: "Darrick J. Wong" <djwong@kernel.org>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/fs-writeback.c

@@ -2197,7 +2197,6 @@ void wb_workfn(struct work_struct *work)
 	long pages_written;
 
 	set_worker_desc("flush-%s", bdi_dev_name(wb->bdi));
-	current->flags |= PF_SWAPWRITE;
 
 	if (likely(!current_is_workqueue_rescuer() ||
 		   !test_bit(WB_registered, &wb->state))) {
@@ -2226,8 +2225,6 @@ void wb_workfn(struct work_struct *work)
 		wb_wakeup(wb);
 	else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
 		wb_wakeup_delayed(wb);
-
-	current->flags &= ~PF_SWAPWRITE;
 }
 
 /*

fs/xfs/libxfs/xfs_btree.c

@@ -2818,7 +2818,7 @@ xfs_btree_split_worker(
 	 * in any way.
 	 */
 	if (args->kswapd)
-		new_pflags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
+		new_pflags |= PF_MEMALLOC | PF_KSWAPD;
 
 	current_set_flags_nested(&pflags, new_pflags);
 	xfs_trans_set_context(args->cur->bc_tp);

include/linux/sched.h

@@ -1689,7 +1689,6 @@ extern struct pid *cad_pid;
 						 * I am cleaning dirty pages from some other bdi. */
 #define PF_KTHREAD		0x00200000	/* I am a kernel thread */
 #define PF_RANDOMIZE		0x00400000	/* Randomize virtual address space */
-#define PF_SWAPWRITE		0x00800000	/* Allowed to write to swap */
 #define PF_NO_SETAFFINITY	0x04000000	/* Userland is not allowed to meddle with cpus_mask */
 #define PF_MCE_EARLY		0x08000000      /* Early kill for mce process policy */
 #define PF_MEMALLOC_PIN		0x10000000	/* Allocation context constrained to zones which allow long term pinning. */

mm/migrate.c

@@ -1350,7 +1350,6 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 	bool is_thp = false;
 	struct page *page;
 	struct page *page2;
-	int swapwrite = current->flags & PF_SWAPWRITE;
 	int rc, nr_subpages;
 	LIST_HEAD(ret_pages);
 	LIST_HEAD(thp_split_pages);
@@ -1359,9 +1358,6 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 
 	trace_mm_migrate_pages_start(mode, reason);
 
-	if (!swapwrite)
-		current->flags |= PF_SWAPWRITE;
-
 thp_subpage_migration:
 	for (pass = 0; pass < 10 && (retry || thp_retry); pass++) {
 		retry = 0;
@@ -1516,9 +1512,6 @@ int migrate_pages(struct list_head *from, new_page_t get_new_page,
 	trace_mm_migrate_pages(nr_succeeded, nr_failed_pages, nr_thp_succeeded,
 			       nr_thp_failed, nr_thp_split, mode, reason);
 
-	if (!swapwrite)
-		current->flags &= ~PF_SWAPWRITE;
-
 	if (ret_succeeded)
 		*ret_succeeded = nr_succeeded;
 

mm/vmscan.c

@@ -4457,7 +4457,7 @@ static int kswapd(void *p)
 	 * us from recursively trying to free more memory as we're
 	 * trying to free the first piece of memory in the first place).
 	 */
-	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
+	tsk->flags |= PF_MEMALLOC | PF_KSWAPD;
 	set_freezable();
 
 	WRITE_ONCE(pgdat->kswapd_order, 0);
@@ -4508,7 +4508,7 @@ static int kswapd(void *p)
 			goto kswapd_try_sleep;
 	}
 
-	tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
+	tsk->flags &= ~(PF_MEMALLOC | PF_KSWAPD);
 
 	return 0;
 }
@@ -4749,11 +4749,8 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
 	fs_reclaim_acquire(sc.gfp_mask);
 	/*
 	 * We need to be able to allocate from the reserves for RECLAIM_UNMAP
-	 * and we also need to be able to write out pages for RECLAIM_WRITE
-	 * and RECLAIM_UNMAP.
 	 */
 	noreclaim_flag = memalloc_noreclaim_save();
-	p->flags |= PF_SWAPWRITE;
 	set_task_reclaim_state(p, &sc.reclaim_state);
 
 	if (node_pagecache_reclaimable(pgdat) > pgdat->min_unmapped_pages) {
@@ -4767,7 +4764,6 @@ static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned in
 	}
 
 	set_task_reclaim_state(p, NULL);
-	current->flags &= ~PF_SWAPWRITE;
 	memalloc_noreclaim_restore(noreclaim_flag);
 	fs_reclaim_release(sc.gfp_mask);
 	psi_memstall_leave(&pflags);