On Nov 21, 2021, at 8:15 PM, NeilBrown [off-list ref] wrote:


Various places in the kernel - largely in filesystems - respond to a
memory allocation failure by looping around and re-trying.
Some of these cannot conveniently use __GFP_NOFAIL, for reasons such as:
- a GFP_ATOMIC allocation, which __GFP_NOFAIL doesn't work on
- a need to check for the process being signalled between failures
- the possibility that other recovery actions could be performed
- the allocation is quite deep in support code, and passing down an
  extra flag to say if __GFP_NOFAIL is wanted would be clumsy.

Many of these currently use congestion_wait() which (in almost all
cases) simply waits the given timeout - congestion isn't tracked for
most devices.

It isn't clear what the best delay is for loops, but it is clear that
the various filesystems shouldn't be responsible for choosing a timeout.

This patch introduces memalloc_retry_wait() with takes on that
responsibility.  Code that wants to retry a memory allocation can call
this function passing the GFP flags that were used.  It will wait
however is appropriate.

For now, it only considers __GFP_NORETRY and whatever
gfpflags_allow_blocking() tests.  If blocking is allowed without
__GFP_NORETRY, then alloc_page either made some reclaim progress, or
waited for a while, before failing.  So there is no need for much
further waiting.  memalloc_retry_wait() will wait until the current
jiffie ends.  If this condition is not met, then alloc_page() won't have
waited much if at all.  In that case memalloc_retry_wait() waits about
200ms.  This is the delay that most current loops uses.

linux/sched/mm.h needs to be included in some files now,
but linux/backing-dev.h does not.

Signed-off-by: NeilBrown <redacted>
---

Switched to io_schedule_timeout(), and added some missing #includes.

fs/ext4/extents.c        |  8 +++-----
fs/ext4/inline.c         |  5 ++---
fs/ext4/page-io.c        |  9 +++++----
fs/f2fs/data.c           |  4 ++--
fs/f2fs/gc.c             |  5 ++---
fs/f2fs/inode.c          |  4 ++--
fs/f2fs/node.c           |  4 ++--
fs/f2fs/recovery.c       |  6 +++---
fs/f2fs/segment.c        |  9 +++------
fs/f2fs/super.c          |  5 ++---
fs/xfs/kmem.c            |  3 +--
fs/xfs/xfs_buf.c         |  2 +-
include/linux/sched/mm.h | 26 ++++++++++++++++++++++++++
net/sunrpc/svc_xprt.c    |  3 ++-
14 files changed, 56 insertions(+), 37 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 0ecf819bf189..5582fba36b44 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c

@@ -27,8 +27,8 @@

#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/fiemap.h>
-#include <linux/backing-dev.h>
#include <linux/iomap.h>
+#include <linux/sched/mm.h>
#include "ext4_jbd2.h"
#include "ext4_extents.h"
#include "xattr.h"

@@ -4407,8 +4407,7 @@ int ext4_ext_truncate(handle_t *handle, struct inode *inode)

	err = ext4_es_remove_extent(inode, last_block,
				    EXT_MAX_BLOCKS - last_block);
	if (err == -ENOMEM) {
-		cond_resched();
-		congestion_wait(BLK_RW_ASYNC, HZ/50);
+		memalloc_retry_wait(GFP_ATOMIC);
		goto retry;
	}
	if (err)

@@ -4416,8 +4415,7 @@ int ext4_ext_truncate(handle_t *handle, struct inode *inode)

retry_remove_space:
	err = ext4_ext_remove_space(inode, last_block, EXT_MAX_BLOCKS - 1);
	if (err == -ENOMEM) {
-		cond_resched();
-		congestion_wait(BLK_RW_ASYNC, HZ/50);
+		memalloc_retry_wait(GFP_ATOMIC);
		goto retry_remove_space;
	}
	return err;

diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c
index 39a1ab129fdc..635bcf68a67e 100644
--- a/fs/ext4/inline.c
+++ b/fs/ext4/inline.c

@@ -7,7 +7,7 @@

#include <linux/iomap.h>
#include <linux/fiemap.h>
#include <linux/iversion.h>
-#include <linux/backing-dev.h>
+#include <linux/sched/mm.h>

#include "ext4_jbd2.h"
#include "ext4.h"

@@ -1929,8 +1929,7 @@ int ext4_inline_data_truncate(struct inode *inode, int *has_inline)

retry:
			err = ext4_es_remove_extent(inode, 0, EXT_MAX_BLOCKS);
			if (err == -ENOMEM) {
-				cond_resched();
-				congestion_wait(BLK_RW_ASYNC, HZ/50);
+				memalloc_retry_wait(GFP_ATOMIC);
				goto retry;
			}
			if (err)

diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
index 9cb261714991..1d370364230e 100644
--- a/fs/ext4/page-io.c
+++ b/fs/ext4/page-io.c

@@ -24,7 +24,7 @@

#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/mm.h>
-#include <linux/backing-dev.h>
+#include <linux/sched/mm.h>

#include "ext4_jbd2.h"
#include "xattr.h"

@@ -523,12 +523,13 @@ int ext4_bio_write_page(struct ext4_io_submit *io,

			ret = PTR_ERR(bounce_page);
			if (ret == -ENOMEM &&
			    (io->io_bio || wbc->sync_mode == WB_SYNC_ALL)) {
-				gfp_flags = GFP_NOFS;
+				gfp_t new_gfp_flags = GFP_NOFS;
				if (io->io_bio)
					ext4_io_submit(io);
				else
-					gfp_flags |= __GFP_NOFAIL;
-				congestion_wait(BLK_RW_ASYNC, HZ/50);
+					new_gfp_flags |= __GFP_NOFAIL;
+				memalloc_retry_wait(gfp_flags);
+				gfp_flags = new_gfp_flags;
				goto retry_encrypt;
			}

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 9f754aaef558..aacf5e4dcc57 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c

@@ -8,9 +8,9 @@

#include <linux/fs.h>
#include <linux/f2fs_fs.h>
#include <linux/buffer_head.h>
+#include <linux/sched/mm.h>
#include <linux/mpage.h>
#include <linux/writeback.h>
-#include <linux/backing-dev.h>
#include <linux/pagevec.h>
#include <linux/blkdev.h>
#include <linux/bio.h>

@@ -2542,7 +2542,7 @@ int f2fs_encrypt_one_page(struct f2fs_io_info *fio)

		/* flush pending IOs and wait for a while in the ENOMEM case */
		if (PTR_ERR(fio->encrypted_page) == -ENOMEM) {
			f2fs_flush_merged_writes(fio->sbi);
-			congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
+			memalloc_retry_wait(GFP_NOFS);
			gfp_flags |= __GFP_NOFAIL;
			goto retry_encrypt;
		}

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index a946ce0ead34..374bbb5294d9 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c

@@ -7,7 +7,6 @@
 */

#include <linux/fs.h>
#include <linux/module.h>
-#include <linux/backing-dev.h>
#include <linux/init.h>
#include <linux/f2fs_fs.h>
#include <linux/kthread.h>

@@ -15,6 +14,7 @@

#include <linux/freezer.h>
#include <linux/sched/signal.h>
#include <linux/random.h>
+#include <linux/sched/mm.h>

#include "f2fs.h"
#include "node.h"

@@ -1375,8 +1375,7 @@ static int move_data_page(struct inode *inode, block_t bidx, int gc_type,

		if (err) {
			clear_page_private_gcing(page);
			if (err == -ENOMEM) {
-				congestion_wait(BLK_RW_ASYNC,
-						DEFAULT_IO_TIMEOUT);
+				memalloc_retry_wait(GFP_NOFS);
				goto retry;
			}
			if (is_dirty)

diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
index 0f8b2df3e1e0..4c11254a07d4 100644
--- a/fs/f2fs/inode.c
+++ b/fs/f2fs/inode.c

@@ -8,8 +8,8 @@

#include <linux/fs.h>
#include <linux/f2fs_fs.h>
#include <linux/buffer_head.h>
-#include <linux/backing-dev.h>
#include <linux/writeback.h>
+#include <linux/sched/mm.h>

#include "f2fs.h"
#include "node.h"

@@ -562,7 +562,7 @@ struct inode *f2fs_iget_retry(struct super_block *sb, unsigned long ino)

	inode = f2fs_iget(sb, ino);
	if (IS_ERR(inode)) {
		if (PTR_ERR(inode) == -ENOMEM) {
-			congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
+			memalloc_retry_wait(GFP_NOFS);
			goto retry;
		}
	}

diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 556fcd8457f3..219506ca9a97 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c

@@ -8,7 +8,7 @@

#include <linux/fs.h>
#include <linux/f2fs_fs.h>
#include <linux/mpage.h>
-#include <linux/backing-dev.h>
+#include <linux/sched/mm.h>
#include <linux/blkdev.h>
#include <linux/pagevec.h>
#include <linux/swap.h>

@@ -2750,7 +2750,7 @@ int f2fs_recover_inode_page(struct f2fs_sb_info *sbi, struct page *page)

retry:
	ipage = f2fs_grab_cache_page(NODE_MAPPING(sbi), ino, false);
	if (!ipage) {
-		congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
+		memalloc_retry_wait(GFP_NOFS);
		goto retry;
	}

diff --git a/fs/f2fs/recovery.c b/fs/f2fs/recovery.c
index 6a1b4668d933..d1664a0567ef 100644
--- a/fs/f2fs/recovery.c
+++ b/fs/f2fs/recovery.c

@@ -8,6 +8,7 @@

#include <asm/unaligned.h>
#include <linux/fs.h>
#include <linux/f2fs_fs.h>
+#include <linux/sched/mm.h>
#include "f2fs.h"
#include "node.h"
#include "segment.h"

@@ -587,7 +588,7 @@ static int do_recover_data(struct f2fs_sb_info *sbi, struct inode *inode,

	err = f2fs_get_dnode_of_data(&dn, start, ALLOC_NODE);
	if (err) {
		if (err == -ENOMEM) {
-			congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
+			memalloc_retry_wait(GFP_NOFS);
			goto retry_dn;
		}
		goto out;

@@ -670,8 +671,7 @@ static int do_recover_data(struct f2fs_sb_info *sbi, struct inode *inode,

			err = check_index_in_prev_nodes(sbi, dest, &dn);
			if (err) {
				if (err == -ENOMEM) {
-					congestion_wait(BLK_RW_ASYNC,
-							DEFAULT_IO_TIMEOUT);
+					memalloc_retry_wait(GFP_NOFS);
					goto retry_prev;
				}
				goto err;

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index df9ed75f0b7a..40fdb4a8daeb 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c

@@ -9,6 +9,7 @@

#include <linux/f2fs_fs.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
+#include <linux/sched/mm.h>
#include <linux/prefetch.h>
#include <linux/kthread.h>
#include <linux/swap.h>

@@ -245,9 +246,7 @@ static int __revoke_inmem_pages(struct inode *inode,

								LOOKUP_NODE);
			if (err) {
				if (err == -ENOMEM) {
-					congestion_wait(BLK_RW_ASYNC,
-							DEFAULT_IO_TIMEOUT);
-					cond_resched();
+					memalloc_retry_wait(GFP_NOFS);
					goto retry;
				}
				err = -EAGAIN;

@@ -424,9 +423,7 @@ static int __f2fs_commit_inmem_pages(struct inode *inode)

			err = f2fs_do_write_data_page(&fio);
			if (err) {
				if (err == -ENOMEM) {
-					congestion_wait(BLK_RW_ASYNC,
-							DEFAULT_IO_TIMEOUT);
-					cond_resched();
+					memalloc_retry_wait(GFP_NOFS);
					goto retry;
				}
				unlock_page(page);

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 040b6d02e1d8..3bace24f8800 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c

@@ -8,9 +8,9 @@

#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
+#include <linux/sched/mm.h>
#include <linux/statfs.h>
#include <linux/buffer_head.h>
-#include <linux/backing-dev.h>
#include <linux/kthread.h>
#include <linux/parser.h>
#include <linux/mount.h>

@@ -2415,8 +2415,7 @@ static ssize_t f2fs_quota_read(struct super_block *sb, int type, char *data,

		page = read_cache_page_gfp(mapping, blkidx, GFP_NOFS);
		if (IS_ERR(page)) {
			if (PTR_ERR(page) == -ENOMEM) {
-				congestion_wait(BLK_RW_ASYNC,
-						DEFAULT_IO_TIMEOUT);
+				memalloc_retry_wait(GFP_NOFS);
				goto repeat;
			}
			set_sbi_flag(F2FS_SB(sb), SBI_QUOTA_NEED_REPAIR);

diff --git a/fs/xfs/kmem.c b/fs/xfs/kmem.c
index 6f49bf39183c..c557a030acfe 100644
--- a/fs/xfs/kmem.c
+++ b/fs/xfs/kmem.c

@@ -4,7 +4,6 @@
 * All Rights Reserved.
 */

#include "xfs.h"
-#include <linux/backing-dev.h>
#include "xfs_message.h"
#include "xfs_trace.h"

@@ -26,6 +25,6 @@ kmem_alloc(size_t size, xfs_km_flags_t flags)

	"%s(%u) possible memory allocation deadlock size %u in %s (mode:0x%x)",
				current->comm, current->pid,
				(unsigned int)size, __func__, lflags);
-		congestion_wait(BLK_RW_ASYNC, HZ/50);
+		memalloc_retry_wait(lflags);
	} while (1);
}

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index 631c5a61d89b..6c45e3fa56f4 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c

@@ -394,7 +394,7 @@ xfs_buf_alloc_pages(

		}

		XFS_STATS_INC(bp->b_mount, xb_page_retries);
-		congestion_wait(BLK_RW_ASYNC, HZ / 50);
+		memalloc_retry_wait(gfp_mask);
	}
	return 0;
}

diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index aca874d33fe6..aa5f09ca5bcf 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h

@@ -214,6 +214,32 @@ static inline void fs_reclaim_acquire(gfp_t gfp_mask) { }

static inline void fs_reclaim_release(gfp_t gfp_mask) { }
#endif

+/* Any memory-allocation retry loop should use
+ * memalloc_retry_wait(), and pass the flags for the most
+ * constrained allocation attempt that might have failed.
+ * This provides useful documentation of where loops are,

+ * and a central place to fine tune the waiting as the MM
+ * implementation changes.
+ */
+static inline void memalloc_retry_wait(gfp_t gfp_flags)
+{
+	/* We use io_schedule_timeout because waiting for memory
+	 * typically included waiting for dirty pages to be
+	 * written out, which requires IO.
+	 */
+	__set_current_state(TASK_UNINTERRUPTIBLE);
+	gfp_flags = current_gfp_context(gfp_flags);
+	if (gfpflags_allow_blocking(gfp_flags) &&
+	    !(gfp_flags & __GFP_NORETRY))
+		/* Probably waited already, no need for much more */
+		io_schedule_timeout(1);
+	else
+		/* Probably didn't wait, and has now released a lock,
+		 * so now is a good time to wait
+		 */
+		io_schedule_timeout(HZ/50);
+}
+
/**
 * might_alloc - Mark possible allocation sites
 * @gfp_mask: gfp_t flags that would be used to allocate

diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 1e99ba1b9d72..9cb18b822ab2 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c

@@ -6,6 +6,7 @@
 */

#include <linux/sched.h>
+#include <linux/sched/mm.h>
#include <linux/errno.h>
#include <linux/freezer.h>
#include <linux/kthread.h>

@@ -688,7 +689,7 @@ static int svc_alloc_arg(struct svc_rqst *rqstp)

			return -EINTR;
		}
		trace_svc_alloc_arg_err(pages);
-		schedule_timeout(msecs_to_jiffies(500));
+		memalloc_retry_wait(GFP_KERNEL);
	}
	rqstp->rq_page_end = &rqstp->rq_pages[pages];
	rqstp->rq_pages[pages] = NULL; /* this might be seen in nfsd_splice_actor() */
-- 
2.33.1