On 7/27/23 17:35, Miklos Szeredi wrote:
On Thu, 27 Jul 2023 at 10:13, Jaco Kroon <jaco@xxxxxxxxx> wrote:This patch does not mess with the caching infrastructure like the previous one, which we believe caused excessive CPU and broke directory listings in some cases. This version only affects the uncached read, which then during parse adds an entry at a time to the cached structures by way of copying, and as such, we believe this should be sufficient. We're still seeing cases where getdents64 takes ~10s (this was the case in any case without this patch, the difference now that we get ~500 entries for that time rather than the 14-18 previously). We believe that that latency is introduced on glusterfs side and is under separate discussion with the glusterfs developers. This is still a compile-time option, but a working one compared to previous patch. For now this works, but it's not recommended for merge (as per email discussion). This still uses alloc_pages rather than kvmalloc/kvfree. Signed-off-by: Jaco Kroon <jaco@xxxxxxxxx> --- fs/fuse/Kconfig | 16 ++++++++++++++++ fs/fuse/readdir.c | 18 ++++++++++++------ 2 files changed, 28 insertions(+), 6 deletions(-) diff --git a/fs/fuse/Kconfig b/fs/fuse/Kconfig index 038ed0b9aaa5..0783f9ee5cd3 100644 --- a/fs/fuse/Kconfig +++ b/fs/fuse/Kconfig @@ -18,6 +18,22 @@ config FUSE_FS If you want to develop a userspace FS, or if you want to use a filesystem based on FUSE, answer Y or M. +config FUSE_READDIR_ORDER + int + range 0 5 + default 5 + help + readdir performance varies greatly depending on the size of the read. + Larger buffers results in larger reads, thus fewer reads and higher + performance in return. + + You may want to reduce this value on seriously constrained memory + systems where 128KiB (assuming 4KiB pages) cache pages is not ideal. + + This value reprents the order of the number of pages to allocate (ie, + the shift value). A value of 0 is thus 1 page (4KiB) where 5 is 32 + pages (128KiB). + config CUSE tristate "Character device in Userspace support" depends on FUSE_FS diff --git a/fs/fuse/readdir.c b/fs/fuse/readdir.c index dc603479b30e..47cea4d91228 100644 --- a/fs/fuse/readdir.c +++ b/fs/fuse/readdir.c @@ -13,6 +13,12 @@ #include <linux/pagemap.h> #include <linux/highmem.h> +#define READDIR_PAGES_ORDER CONFIG_FUSE_READDIR_ORDER +#define READDIR_PAGES (1 << READDIR_PAGES_ORDER) +#define READDIR_PAGES_SIZE (PAGE_SIZE << READDIR_PAGES_ORDER) +#define READDIR_PAGES_MASK (READDIR_PAGES_SIZE - 1) +#define READDIR_PAGES_SHIFT (PAGE_SHIFT + READDIR_PAGES_ORDER) + static bool fuse_use_readdirplus(struct inode *dir, struct dir_context *ctx) { struct fuse_conn *fc = get_fuse_conn(dir); @@ -328,25 +334,25 @@ static int fuse_readdir_uncached(struct file *file, struct dir_context *ctx) struct fuse_mount *fm = get_fuse_mount(inode); struct fuse_io_args ia = {}; struct fuse_args_pages *ap = &ia.ap; - struct fuse_page_desc desc = { .length = PAGE_SIZE }; + struct fuse_page_desc desc = { .length = READDIR_PAGES_SIZE };Does this really work? I would've thought we are relying on single page lengths somewhere.u64 attr_version = 0; bool locked; - page = alloc_page(GFP_KERNEL); + page = alloc_pages(GFP_KERNEL, READDIR_PAGES_ORDER); if (!page) return -ENOMEM; plus = fuse_use_readdirplus(inode, ctx); ap->args.out_pages = true; - ap->num_pages = 1; + ap->num_pages = READDIR_PAGES;No. This is the array lenght, which is 1. This is the hack I guess, which makes the above trick work.
Hmm, ap->num_pages / ap->pages[] is used in fuse_copy_pages, but so is ap->descs[] - shouldn't the patch caused an out-of-bound access?
Out of interest, would you mind to explain how the hack worked? Thanks, Bernd
