From:   Chuck Lever III <chuck.lever@oracle.com>
To:     Neil Brown <neilb@suse.de>
CC:     Dave Chinner <david@fromorbit.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>, Theodore Ts'o <tytso@mit.edu>,
        "linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>,
        Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <chao@kernel.org>,
        "Darrick J. Wong" <djwong@kernel.org>,
        "linux-xfs@vger.kernel.org" <linux-xfs@vger.kernel.org>,
        "linux-f2fs-devel@lists.sourceforge.net" 
        <linux-f2fs-devel@lists.sourceforge.net>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2] MM: introduce memalloc_retry_wait()
Thread-Topic: [PATCH v2] MM: introduce memalloc_retry_wait()
Thread-Index: AQHX3z5z7K9wSNEtN0mv2FiO5P+VlqwPppQA
Date:   Mon, 22 Nov 2021 15:06:33 +0000
Message-ID: <286F4A23-74EC-44E7-8734-CD378C2B5298@oracle.com>
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> On Nov 21, 2021, at 8:15 PM, NeilBrown <neilb@suse.de> wrote:
>=20
>=20
> 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.
>=20
> Many of these currently use congestion_wait() which (in almost all
> cases) simply waits the given timeout - congestion isn't tracked for
> most devices.
>=20
> 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.
>=20
> 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.
>=20
> 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.
>=20
> linux/sched/mm.h needs to be included in some files now,
> but linux/backing-dev.h does not.
>=20
> Signed-off-by: NeilBrown <neilb@suse.de>
> ---
>=20
> Switched to io_schedule_timeout(), and added some missing #includes.
>=20
> 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(-)
>=20
> 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 inod=
e *inode)
> 	err =3D ext4_es_remove_extent(inode, last_block,
> 				    EXT_MAX_BLOCKS - last_block);
> 	if (err =3D=3D -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 inod=
e *inode)
> retry_remove_space:
> 	err =3D ext4_ext_remove_space(inode, last_block, EXT_MAX_BLOCKS - 1);
> 	if (err =3D=3D -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>
>=20
> #include "ext4_jbd2.h"
> #include "ext4.h"
> @@ -1929,8 +1929,7 @@ int ext4_inline_data_truncate(struct inode *inode, =
int *has_inline)
> retry:
> 			err =3D ext4_es_remove_extent(inode, 0, EXT_MAX_BLOCKS);
> 			if (err =3D=3D -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>
>=20
> #include "ext4_jbd2.h"
> #include "xattr.h"
> @@ -523,12 +523,13 @@ int ext4_bio_write_page(struct ext4_io_submit *io,
> 			ret =3D PTR_ERR(bounce_page);
> 			if (ret =3D=3D -ENOMEM &&
> 			    (io->io_bio || wbc->sync_mode =3D=3D WB_SYNC_ALL)) {
> -				gfp_flags =3D GFP_NOFS;
> +				gfp_t new_gfp_flags =3D GFP_NOFS;
> 				if (io->io_bio)
> 					ext4_io_submit(io);
> 				else
> -					gfp_flags |=3D __GFP_NOFAIL;
> -				congestion_wait(BLK_RW_ASYNC, HZ/50);
> +					new_gfp_flags |=3D __GFP_NOFAIL;
> +				memalloc_retry_wait(gfp_flags);
> +				gfp_flags =3D new_gfp_flags;
> 				goto retry_encrypt;
> 			}
>=20
> 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) =3D=3D -ENOMEM) {
> 			f2fs_flush_merged_writes(fio->sbi);
> -			congestion_wait(BLK_RW_ASYNC, DEFAULT_IO_TIMEOUT);
> +			memalloc_retry_wait(GFP_NOFS);
> 			gfp_flags |=3D __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>
>=20
> #include "f2fs.h"
> #include "node.h"
> @@ -1375,8 +1375,7 @@ static int move_data_page(struct inode *inode, bloc=
k_t bidx, int gc_type,
> 		if (err) {
> 			clear_page_private_gcing(page);
> 			if (err =3D=3D -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>
>=20
> #include "f2fs.h"
> #include "node.h"
> @@ -562,7 +562,7 @@ struct inode *f2fs_iget_retry(struct super_block *sb,=
 unsigned long ino)
> 	inode =3D f2fs_iget(sb, ino);
> 	if (IS_ERR(inode)) {
> 		if (PTR_ERR(inode) =3D=3D -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 *sb=
i, struct page *page)
> retry:
> 	ipage =3D 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;
> 	}
>=20
> 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 =3D f2fs_get_dnode_of_data(&dn, start, ALLOC_NODE);
> 	if (err) {
> 		if (err =3D=3D -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 =3D check_index_in_prev_nodes(sbi, dest, &dn);
> 			if (err) {
> 				if (err =3D=3D -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 =3D=3D -ENOMEM) {
> -					congestion_wait(BLK_RW_ASYNC,
> -							DEFAULT_IO_TIMEOUT);
> -					cond_resched();
> +					memalloc_retry_wait(GFP_NOFS);
> 					goto retry;
> 				}
> 				err =3D -EAGAIN;
> @@ -424,9 +423,7 @@ static int __f2fs_commit_inmem_pages(struct inode *in=
ode)
> 			err =3D f2fs_do_write_data_page(&fio);
> 			if (err) {
> 				if (err =3D=3D -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 =3D read_cache_page_gfp(mapping, blkidx, GFP_NOFS);
> 		if (IS_ERR(page)) {
> 			if (PTR_ERR(page) =3D=3D -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"
>=20
> @@ -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(
> 		}
>=20
> 		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
>=20
> +/* 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,

"useful documentation" is a good thing, but to me that means
there's some auditing mechanism like a trace point. Getting
to this function seems like an exceptional event that should
be noted externally.

If memalloc_retry_wait() had a trace point, I'd be inclined
to remove trace_svc_alloc_arg_err().

(This comment is not an objection to your patch).


> + * 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 =3D 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 @@
>  */
>=20
> #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 =3D &rqstp->rq_pages[pages];
> 	rqstp->rq_pages[pages] =3D NULL; /* this might be seen in nfsd_splice_ac=
tor() */
> --=20
> 2.33.1
>=20

--
Chuck Lever