From: "Benjamin Coddington" <bcodding@redhat.com>
To: "Trond Myklebust" <trondmy@hammerspace.com>
Cc: linux-nfs@vger.kernel.org, dwysocha@redhat.com
Subject: Re: [PATCH v5 00/22] Readdir enhancements
Date: Thu, 12 Nov 2020 15:23:32 -0500 [thread overview]
Message-ID: <FF04DA98-C072-4C92-ABF9-41FE6ECB10B5@redhat.com> (raw)
In-Reply-To: <DD8B2AD2-34BF-4751-A01A-3E10677EB8E7@redhat.com>
On 12 Nov 2020, at 14:09, Benjamin Coddington wrote:
> On 12 Nov 2020, at 14:04, Trond Myklebust wrote:
>
>> On Thu, 2020-11-12 at 13:39 -0500, Benjamin Coddington wrote:
>>>
>>>
>>> On 12 Nov 2020, at 13:26, Trond Myklebust wrote:
>>>
>>>> On Thu, 2020-11-12 at 16:51 +0000, Trond Myklebust wrote:
>>>>>
>>>>> I was going to ask you if perhaps reverting Scott's commit
>>>>> 07b5ce8ef2d8
>>>>> ("NFS: Make nfs_readdir revalidate less often") might help here?
>>>>> My thinking is that will trigger more cache invalidations when
>>>>> the
>>>>> directory is changing underneath us, and will now trigger
>>>>> uncached
>>>>> readdir in those situations.
>>>>>
>>>>>>
>>>>
>>>> IOW, the suggestion would be to apply something like the following
>>>> on
>>>> top of the existing readdir patchset:
>>>
>>> I'm all for this approach, but - I'm rarely seeing the mapping-
>>>> nrpages == 0
>>> since the cache is dropped by a process in nfs_readdir() that
>>> immediately
>>> starts filling the cache again.
>>
>> That's why I moved the check in readdir_search_pagecache. Unless that
>> process has set desc->dir_cookie == 0, then that should prevent the
>> refilling.
>
> My pathological benchmarking does send another process in with
> desc->dir_cookie == 0.
>
> I'm doing fork(), while(getdents) every second with acdirmin=1 and a
> listing
> that takes longer than 1 second to complete uncached, while touching
> the
> directory every second.
As long as I use a buffer > 16k for getdents(), this hack can keep up
with the testcase:
diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index d7a9efd31ecd..ae687662112a 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -78,6 +78,7 @@ static struct nfs_open_dir_context
*alloc_nfs_open_dir_context(struct inode *dir
ctx->attr_gencount = nfsi->attr_gencount;
ctx->dir_cookie = 0;
ctx->dup_cookie = 0;
+ ctx->page_index = 0;
spin_lock(&dir->i_lock);
if (list_empty(&nfsi->open_files) &&
(nfsi->cache_validity & NFS_INO_DATA_INVAL_DEFER))
@@ -150,6 +151,7 @@ struct nfs_readdir_descriptor {
struct page *page;
struct dir_context *ctx;
pgoff_t page_index;
+ pgoff_t last_page_index;
u64 dir_cookie;
u64 last_cookie;
u64 dup_cookie;
@@ -928,7 +930,12 @@ static bool nfs_readdir_dont_search_cache(struct
nfs_readdir_descriptor *desc)
* Default to uncached readdir if the page cache is empty, and
* we're looking for a non-zero cookie in a large directory.
*/
- return desc->dir_cookie != 0 && mapping->nrpages == 0 && size >
dtsize;
+ if (desc->dir_cookie == 0)
+ return false;
+ else if (mapping->nrpages < desc->last_page_index && size >
dtsize)
+ return true;
+
+ return false;
}
/* Search for desc->dir_cookie from the beginning of the page cache */
@@ -936,10 +943,10 @@ static int readdir_search_pagecache(struct
nfs_readdir_descriptor *desc)
{
int res;
- if (nfs_readdir_dont_search_cache(desc))
- return -EBADCOOKIE;
-
do {
+ if (nfs_readdir_dont_search_cache(desc))
+ return -EBADCOOKIE;
+
if (desc->page_index == 0) {
desc->current_index = 0;
desc->prev_index = 0;
@@ -1062,11 +1069,9 @@ static int nfs_readdir(struct file *file, struct
dir_context *ctx)
* to either find the entry with the appropriate number or
* revalidate the cookie.
*/
- if (ctx->pos == 0 || nfs_attribute_cache_expired(inode)) {
- res = nfs_revalidate_mapping(inode, file->f_mapping);
- if (res < 0)
- goto out;
- }
+ res = nfs_revalidate_mapping(inode, file->f_mapping);
+ if (res < 0)
+ goto out;
res = -ENOMEM;
desc = kzalloc(sizeof(*desc), GFP_KERNEL);
@@ -1082,6 +1087,7 @@ static int nfs_readdir(struct file *file, struct
dir_context *ctx)
desc->duped = dir_ctx->duped;
desc->attr_gencount = dir_ctx->attr_gencount;
memcpy(desc->verf, dir_ctx->verf, sizeof(desc->verf));
+ desc->last_page_index = dir_ctx->page_index;
spin_unlock(&file->f_lock);
do {
@@ -1121,6 +1127,8 @@ static int nfs_readdir(struct file *file, struct
dir_context *ctx)
dir_ctx->duped = desc->duped;
dir_ctx->attr_gencount = desc->attr_gencount;
memcpy(dir_ctx->verf, desc->verf, sizeof(dir_ctx->verf));
+ if (desc->page_index > dir_ctx->page_index)
+ dir_ctx->page_index = desc->page_index;
spin_unlock(&file->f_lock);
kfree(desc);
diff --git a/include/linux/nfs_fs.h b/include/linux/nfs_fs.h
index 681ed98e4ba8..ad1f8e9a22e6 100644
--- a/include/linux/nfs_fs.h
+++ b/include/linux/nfs_fs.h
@@ -98,6 +98,7 @@ struct nfs_open_dir_context {
__u64 dir_cookie;
__u64 dup_cookie;
signed char duped;
+ pgoff_t page_index;
};
/*
Here's the testcase I'm using:
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/syscall.h>
#include <sys/time.h>
/*
* mkdir /exports/10k_dentries
* for i in {1..10000}; do printf "/exports/10k_dentries/file%.12d\n"
$i; done | xargs touch
*/
#define DIR "/mnt/fedora/10k_dentries"
#define BUF_SIZE 1024 * 16
void evict_pagecache() {
int dir_fd = open(DIR, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC);
posix_fadvise(dir_fd, 0, 0, POSIX_FADV_DONTNEED);
close(dir_fd);
}
/* call getdents64() until no more, return time taken */
int listdir() {
struct timeval tvs, tve;
char buf[BUF_SIZE];
int dir_fd = open(DIR, O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC);
gettimeofday(&tvs, NULL);
while (syscall(SYS_getdents, dir_fd, buf, BUF_SIZE)) { }
gettimeofday(&tve, NULL);
return tve.tv_sec - tvs.tv_sec;
}
int main(int argc, char **argv)
{
evict_pagecache();
while (1) {
if (!fork()) {
int secs;
printf("pid %d starts..\n", getpid());
fflush(stdout);
secs = listdir();
printf("pid %d done %d seconds\n", getpid(), secs);
fflush(stdout);
return 0;
}
sleep (1);
}
}
Ben
next prev parent reply other threads:[~2020-11-12 20:23 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-10 21:37 [PATCH v5 00/22] Readdir enhancements trondmy
2020-11-10 21:37 ` [PATCH v5 01/22] NFS: Remove unnecessary inode locking in nfs_llseek_dir() trondmy
2020-11-10 21:37 ` [PATCH v5 02/22] NFS: Remove unnecessary inode lock in nfs_fsync_dir() trondmy
2020-11-10 21:37 ` [PATCH v5 03/22] NFSv4.2: condition READDIR's mask for security label based on LSM state trondmy
2020-11-10 21:37 ` [PATCH v5 04/22] NFS: Ensure contents of struct nfs_open_dir_context are consistent trondmy
2020-11-10 21:37 ` [PATCH v5 05/22] NFS: Clean up readdir struct nfs_cache_array trondmy
2020-11-10 21:37 ` [PATCH v5 06/22] NFS: Clean up nfs_readdir_page_filler() trondmy
2020-11-10 21:37 ` [PATCH v5 07/22] NFS: Clean up directory array handling trondmy
2020-11-10 21:37 ` [PATCH v5 08/22] NFS: Don't discard readdir results trondmy
2020-11-10 21:37 ` [PATCH v5 09/22] NFS: Remove unnecessary kmap in nfs_readdir_xdr_to_array() trondmy
2020-11-10 21:37 ` [PATCH v5 10/22] NFS: Replace kmap() with kmap_atomic() in nfs_readdir_search_array() trondmy
2020-11-10 21:37 ` [PATCH v5 11/22] NFS: Simplify struct nfs_cache_array_entry trondmy
2020-11-10 21:37 ` [PATCH v5 12/22] NFS: Support larger readdir buffers trondmy
2020-11-10 21:37 ` [PATCH v5 13/22] NFS: More readdir cleanups trondmy
2020-11-10 21:37 ` [PATCH v5 14/22] NFS: nfs_do_filldir() does not return a value trondmy
2020-11-10 21:37 ` [PATCH v5 15/22] NFS: Reduce readdir stack usage trondmy
2020-11-10 21:37 ` [PATCH v5 16/22] NFS: Cleanup to remove nfs_readdir_descriptor_t typedef trondmy
2020-11-10 21:37 ` [PATCH v5 17/22] NFS: Allow the NFS generic code to pass in a verifier to readdir trondmy
2020-11-10 21:37 ` [PATCH v5 18/22] NFS: Handle NFS4ERR_NOT_SAME and NFSERR_BADCOOKIE from readdir calls trondmy
2020-11-10 21:37 ` [PATCH v5 19/22] NFS: Improve handling of directory verifiers trondmy
2020-11-10 21:37 ` [PATCH v5 20/22] NFS: Optimisations for monotonically increasing readdir cookies trondmy
2020-11-10 21:37 ` [PATCH v5 21/22] NFS: Reduce number of RPC calls when doing uncached readdir trondmy
2020-11-10 21:37 ` [PATCH v5 22/22] NFS: Do uncached readdir when we're seeking a cookie in an empty page cache trondmy
2020-11-11 22:15 ` [PATCH v5 00/22] Readdir enhancements David Wysochanski
2020-11-12 11:41 ` David Wysochanski
2020-11-12 15:34 ` Guy Keren
2020-11-12 16:54 ` Trond Myklebust
2020-11-12 16:51 ` Trond Myklebust
2020-11-12 18:26 ` Trond Myklebust
2020-11-12 18:39 ` Benjamin Coddington
2020-11-12 18:49 ` Benjamin Coddington
2020-11-12 19:04 ` Trond Myklebust
2020-11-12 19:09 ` Benjamin Coddington
2020-11-12 20:23 ` Benjamin Coddington [this message]
2020-11-13 11:09 ` Mkrtchyan, Tigran
2020-11-14 13:32 ` David Wysochanski
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