Message-id: <163712329077.13692.12796971766360881401@noble.neil.brown.name>
Date:   Wed, 17 Nov 2021 15:28:10 +1100
From:   "NeilBrown" <neilb@...e.de>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>
Cc:     "Theodore Ts'o" <tytso@....edu>, linux-ext4@...r.kernel.org,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        "Darrick J. Wong" <djwong@...nel.org>, linux-xfs@...r.kernel.org,
        Chuck Lever <chuck.lever@...cle.com>,
        linux-f2fs-devel@...ts.sourceforge.net, linux-nfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] MM: introduce memalloc_retry_wait()


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 the __GFP_DIRECT_RECLAIM and __GFP_NORETRY
flags.  If DIRECT_RECLAIM is set 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.  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 <neilb@...e.de>
---

I could split this up by filesystems if people prefer that, but they we
would have to wait for the -mm patch to land before they could be
applied.  What do people think?  Can Andrew just collected acked-bys?

Thanks,
NeilBrown


 fs/ext4/extents.c        |  8 +++-----
 fs/ext4/inline.c         |  5 ++---
 fs/ext4/page-io.c        |  9 +++++----
 fs/f2fs/data.c           |  3 +--
 fs/f2fs/gc.c             |  5 ++---
 fs/f2fs/inode.c          |  4 ++--
 fs/f2fs/node.c           |  3 +--
 fs/f2fs/recovery.c       |  6 +++---
 fs/f2fs/segment.c        |  8 ++------
 fs/f2fs/super.c          |  4 +---
 fs/xfs/kmem.c            |  3 +--
 fs/xfs/xfs_buf.c         |  2 +-
 include/linux/sched/mm.h | 21 +++++++++++++++++++++
 net/sunrpc/svc_xprt.c    |  2 +-
 14 files changed, 46 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..48b80e7ec35e 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -10,7 +10,6 @@
 #include <linux/buffer_head.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 +2541,7 @@ 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..f8646c29e00b 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -8,7 +8,6 @@
 #include <linux/fs.h>
 #include <linux/f2fs_fs.h>
 #include <linux/mpage.h>
-#include <linux/backing-dev.h>
 #include <linux/blkdev.h>
 #include <linux/pagevec.h>
 #include <linux/swap.h>
@@ -2750,7 +2749,7 @@ 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..6140eada8607 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -245,9 +245,7 @@ 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 +422,7 @@ 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..be9006d6213f 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -10,7 +10,6 @@
 #include <linux/fs.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 +2414,7 @@ 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..f2f2a5b28808 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -214,6 +214,27 @@ 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)
+{
+	gfp_flags = current_gfp_context(gfp_flags);
+	if ((gfp_flags & __GFP_DIRECT_RECLAIM) &&
+	    !(gfp_flags & __GFP_NORETRY))
+		/* Probably waited already, no need for much more */
+		schedule_timeout_uninterruptible(1);
+	else
+		/* Probably didn't wait, and has now released a lock,
+		 * so now is a good time to wait
+		 */
+		schedule_timeout_uninterruptible(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..f9584e8e8324 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -688,7 +688,7 @@ 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

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