Re: [PATCH] btrfs: raid56: use kzalloc_flex for rbio

[Qu Wenruo]

在 2026/3/9 07:23, Rosen Penev 写道:
Simplifies allocation slightly. Now stripe_pages does not need to be
freed separately.

Added __counted_by for extra runtime analysis.

If that's the only variable sized member this will be a good change.

Unfortunately there are too many pointers for variable sized members, 
all around the old @stripe_pages pointer.

Treating @stripe_pages differently from other doesn't seem good to 
expandability nor readability.

Thanks,
Qu


Signed-off-by: Rosen Penev <ros...@gmail.com>
---
  fs/btrfs/raid56.c |  9 ++++-----
  fs/btrfs/raid56.h | 12 ++++++------
  2 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
index baebd9f733e9..d74ae380265e 100644
--- a/fs/btrfs/raid56.c
+++ b/fs/btrfs/raid56.c
@@ -151,7 +151,6 @@ static void free_raid_bio_pointers(struct btrfs_raid_bio 
*rbio)
  {
        bitmap_free(rbio->error_bitmap);
        bitmap_free(rbio->stripe_uptodate_bitmap);
-       kfree(rbio->stripe_pages);
        kfree(rbio->bio_paddrs);
        kfree(rbio->stripe_paddrs);
        kfree(rbio->finish_pointers);
@@ -1070,10 +1069,11 @@ static struct btrfs_raid_bio *alloc_rbio(struct 
btrfs_fs_info *fs_info,
        ASSERT(real_stripes >= 2);
        ASSERT(real_stripes <= U8_MAX);
  
-	rbio = kzalloc_obj(*rbio, GFP_NOFS);
+       rbio = kzalloc_flex(*rbio, stripe_pages, num_pages, GFP_NOFS);
        if (!rbio)
                return ERR_PTR(-ENOMEM);
-       rbio->stripe_pages = kzalloc_objs(struct page *, num_pages, GFP_NOFS);
+
+       rbio->nr_pages = num_pages;
        rbio->bio_paddrs = kzalloc_objs(phys_addr_t,
                                        num_sectors * sector_nsteps, GFP_NOFS);
        rbio->stripe_paddrs = kzalloc_objs(phys_addr_t,
@@ -1083,7 +1083,7 @@ static struct btrfs_raid_bio *alloc_rbio(struct 
btrfs_fs_info *fs_info,
        rbio->error_bitmap = bitmap_zalloc(num_sectors, GFP_NOFS);
        rbio->stripe_uptodate_bitmap = bitmap_zalloc(num_sectors, GFP_NOFS);
  
-	if (!rbio->stripe_pages || !rbio->bio_paddrs || !rbio->stripe_paddrs ||
+       if (!rbio->bio_paddrs || !rbio->stripe_paddrs ||
            !rbio->finish_pointers || !rbio->error_bitmap || 
!rbio->stripe_uptodate_bitmap) {
                free_raid_bio_pointers(rbio);
                kfree(rbio);
@@ -1102,7 +1102,6 @@ static struct btrfs_raid_bio *alloc_rbio(struct 
btrfs_fs_info *fs_info,
        INIT_LIST_HEAD(&rbio->hash_list);
        btrfs_get_bioc(bioc);
        rbio->bioc = bioc;
-       rbio->nr_pages = num_pages;
        rbio->nr_sectors = num_sectors;
        rbio->real_stripes = real_stripes;
        rbio->stripe_npages = stripe_npages;
diff --git a/fs/btrfs/raid56.h b/fs/btrfs/raid56.h
index 1f463ecf7e41..dbe6b7a2e194 100644
--- a/fs/btrfs/raid56.h
+++ b/fs/btrfs/raid56.h
@@ -194,12 +194,6 @@ struct btrfs_raid_bio {
         * allocated.
         */
  
-	/*
-        * Pointers to pages that we allocated for reading/writing stripes
-        * directly from the disk (including P/Q).
-        */
-       struct page **stripe_pages;
-
        /* Pointers to the sectors in the bio_list, for faster lookup */
        phys_addr_t *bio_paddrs;
  
@@ -230,6 +224,12 @@ struct btrfs_raid_bio {
         * Should only cover data sectors (excluding P/Q sectors).
         */
        unsigned long *csum_bitmap;
+
+       /*
+        * Pointers to pages that we allocated for reading/writing stripes
+        * directly from the disk (including P/Q).
+        */
+       struct page *stripe_pages[] __counted_by(nr_pages);
  };
  
  /*