Little FS "No more free space" on Large Flash

[Ecic2002]

Hello,
I am working on an application where large amount of data are being stored onto a NOR flash. The flash is a W25Q02JV with 2Gb of storage, running little FS. My application works as expected filling a little over half of the flash with data, but runs into issues afterwards. The FS write calls take very long and errors out with little_fs claiming there is no more free space. There is still however 32,769 blocks remaining. I am using the default settings for little_fs parameters. Could I be making some better choices here? I've included some of my debug logs from both startup and runtime. Thank you for any help.

During startup:
...
00> [00:00:01.031,005] <inf> StorageLib: Enter Setup Little FS
00> [00:00:01.031,036] <inf> StorageLib: Area 1 at 0x0 on w25q02jv@0 for 268435456 bytes
00> [00:00:01.031,066] <inf> littlefs: LittleFS version 2.5, disk version 2.0
00> [00:00:01.092,742] <inf> littlefs: FS at w25q02jv@0:0x0 is 65536 0x1000-byte blocks with 512 cycle
00> [00:00:01.092,742] <inf> littlefs: sizes: rd 16 ; pr 16 ; ca 64 ; la 32
00> [00:00:01.248,077] <inf> StorageLib: Filesystem mounted at /lfs
00> [00:00:02.980,407] <inf> StorageLib: /lfs: bsize = 16 ; frsize = 4096 ; blocks = 65536 ; bfree = 32770
00> [00:00:03.130,615] <inf> StorageLib: Attempting to open directory: /lfs
00> [00:00:03.134,704] <inf> StorageLib: Listing directory /lfs ...
00> [00:01:00.086,242] <inf> StorageLib: [FILE] 12F5C425CAA9-669A57.DAT (size = 210248)
00> [00:01:00.188,659] <inf> StorageLib: [FILE] 12F5C425CAA9-669A58.DAT (size = 211314)
00> [00:01:00.291,015] <inf> StorageLib: [FILE] 12F5C425CAA9-669A59.DAT (size = 210002)
00> [00:01:00.393,127] <inf> StorageLib: [FILE] 12F5C425CAA9-669A5A.DAT (size = 210658)
00> [00:01:00.495,147] <inf> StorageLib: [FILE] 12F5C425CAA9-669A5B.DAT (size = 211314)
00> [00:01:00.596,923] <inf> StorageLib: [FILE] 12F5C425CAA9-669A5C.DAT (size = 210412)
...
During runtime:
...
00> [00:01:27.008,605] <inf> System: --- Device started and collecting data ---
00> [00:01:42.999,938] <inf> StorageLib: Opening file: /lfs/12F5C425CAA9-669E78.DAT
00> [00:01:45.201,293] <inf> StorageLib: Header written to file: /lfs/12F5C425CAA9-669E78.DAT
00> [00:14:36.135,070] <err> littlefs: WEST_TOPDIR/modules/fs/littlefs/lfs.c:589: No more free space 32769
00> [00:14:36.135,192] <err> fs: file write error (-28)
00> [00:14:36.136,383] <err> StorageLib: Failed to write sample 100 to file /lfs/12F5C425CAA9-669E78.DAT: -28

[Sigurd Hellesvik]

Hi,

Can you check which parameter is tested when littlefs decides that it is out of space, in the library code?

Regards,
Sigurd Hellesvik

[Ecic2002]

It is failing inside of lfs.c on check of free.ack == 0, here is the code from lfsc:

static int lfs_alloc(lfs_t *lfs, lfs_block_t *block) {
    while (true) {
        while (lfs->free.i != lfs->free.size) {
            lfs_block_t off = lfs->free.i;
            lfs->free.i += 1;
            lfs->free.ack -= 1;

            if (!(lfs->free.buffer[off / 32] & (1U << (off % 32)))) {
                // found a free block
                *block = (lfs->free.off + off) % lfs->cfg->block_count;

                // eagerly find next off so an alloc ack can
                // discredit old lookahead blocks
                while (lfs->free.i != lfs->free.size &&
                        (lfs->free.buffer[lfs->free.i / 32]
                            & (1U << (lfs->free.i % 32)))) {
                    lfs->free.i += 1;
                    lfs->free.ack -= 1;
                }

                return 0;
            }
        }

        // check if we have looked at all blocks since last ack
        if (lfs->free.ack == 0) {
            LFS_ERROR("No more free space %"PRIu32,
                    lfs->free.i + lfs->free.off);
            return LFS_ERR_NOSPC;
        }
...

If I understand correctly, I might be able to increase my lookahead size so that littlefs sepnds more time looking for the next free block? What littlefs parameters could be set to limit fragmentation?

As a side note, restarting the device does regain functionality, but only a short while before getting the memory full error again.

Thank you,
Eric

[Sigurd Hellesvik]

This is a good start!

Ecic2002 said:

If I understand correctly, I might be able to increase my lookahead size so that littlefs sepnds more time looking for the next free block? What littlefs parameters could be set to limit fragmentation?

Lets start by checking one thing first:

What is the start value for ack? Maybe it is initialized lower than expected?
In the same file, this is allocated with lfs_alloc_ack(). What is the start value here? Is it what you would expect for your flash size?