io_uring: use kvmalloc for fixed files

Instead of hand-coded two-level tables for registered files, allocate
them with kvmalloc(). In many cases small enough tables are enough, and
so can be kmalloc()'ed removing an extra memory load and a bunch of bit
logic instructions from the hot path. If the table is larger, we trade
off all the pros with a TLB-assisted memory lookup.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/280421d3b48775dabab773006bb5588c7b2dabc0.1628471125.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 626c2784723de418ac3383c0c5fb4a1e8a4bcf14..f8e6eb9de77658e4e25f7fa49f2858ef3aa3bad1 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -92,13 +92,8 @@
 #define IORING_MAX_CQ_ENTRIES  (2 * IORING_MAX_ENTRIES)
 #define IORING_SQPOLL_CAP_ENTRIES_VALUE 8
 
-/*
- * Shift of 9 is 512 entries, or exactly one page on 64-bit archs
- */
-#define IORING_FILE_TABLE_SHIFT        9
-#define IORING_MAX_FILES_TABLE (1U << IORING_FILE_TABLE_SHIFT)
-#define IORING_FILE_TABLE_MASK (IORING_MAX_FILES_TABLE - 1)
-#define IORING_MAX_FIXED_FILES (64 * IORING_MAX_FILES_TABLE)
+/* 512 entries per page on 64-bit archs, 64 pages max */
+#define IORING_MAX_FIXED_FILES (1U << 15)
 #define IORING_MAX_RESTRICTIONS        (IORING_RESTRICTION_LAST + \
                                 IORING_REGISTER_LAST + IORING_OP_LAST)
 
@@ -235,8 +230,7 @@ struct io_rsrc_put {
 };
 
 struct io_file_table {
-       /* two level table */
-       struct io_fixed_file **files;
+       struct io_fixed_file *files;
 };
 
 struct io_rsrc_node {
@@ -6333,12 +6327,9 @@ static void io_wq_submit_work(struct io_wq_work *work)
 #define FFS_MASK               ~(FFS_ASYNC_READ|FFS_ASYNC_WRITE|FFS_ISREG)
 
 static inline struct io_fixed_file *io_fixed_file_slot(struct io_file_table *table,
-                                                     unsigned i)
+                                                      unsigned i)
 {
-       struct io_fixed_file *table_l2;
-
-       table_l2 = table->files[i >> IORING_FILE_TABLE_SHIFT];
-       return &table_l2[i & IORING_FILE_TABLE_MASK];
+       return &table->files[i];
 }
 
 static inline struct file *io_file_from_index(struct io_ring_ctx *ctx,
@@ -7276,17 +7267,13 @@ fail:
 
 static bool io_alloc_file_tables(struct io_file_table *table, unsigned nr_files)
 {
-       size_t size = nr_files * sizeof(struct io_fixed_file);
-
-       table->files = (struct io_fixed_file **)io_alloc_page_table(size);
+       table->files = kvcalloc(nr_files, sizeof(table->files[0]), GFP_KERNEL);
        return !!table->files;
 }
 
-static void io_free_file_tables(struct io_file_table *table, unsigned nr_files)
+static void io_free_file_tables(struct io_file_table *table)
 {
-       size_t size = nr_files * sizeof(struct io_fixed_file);
-
-       io_free_page_table((void **)table->files, size);
+       kvfree(table->files);
        table->files = NULL;
 }
 
@@ -7311,7 +7298,7 @@ static void __io_sqe_files_unregister(struct io_ring_ctx *ctx)
                        fput(file);
        }
 #endif
-       io_free_file_tables(&ctx->file_table, ctx->nr_user_files);
+       io_free_file_tables(&ctx->file_table);
        io_rsrc_data_free(ctx->file_data);
        ctx->file_data = NULL;
        ctx->nr_user_files = 0;
@@ -7779,7 +7766,7 @@ out_fput:
                if (file)
                        fput(file);
        }
-       io_free_file_tables(&ctx->file_table, nr_args);
+       io_free_file_tables(&ctx->file_table);
        ctx->nr_user_files = 0;
 out_free:
        io_rsrc_data_free(ctx->file_data);