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    SubjectRe: [PATCH AUTOSEL 5.10 116/116] ext4: allow to change s_last_trim_minblks via sysfs
    Why was this selected? It is a new feature not a fix, it's not marked
    for a stable kernel and moreover it's incomplete
    (2327fb2e23416cfb2795ccca2f77d4d65925be99 is a prerequisite).

    I have the same question for the patches for 5.15 and 5.16.

    I think we should either drop it, or at the very least include the above
    mentioned commit as well.

    Thanks!
    -Lukas

    On Mon, Jan 17, 2022 at 09:40:07PM -0500, Sasha Levin wrote:
    > From: Lukas Czerner <lczerner@redhat.com>
    >
    > [ Upstream commit 4a69aecbfb30a3fc85bf8028386c047d5607a97a ]
    >
    > Ext4 has an optimization mechanism for batched disacrd (FITRIM) that
    > should help speed up subsequent calls of FITRIM ioctl by skipping the
    > groups that were previously trimmed. However because the FITRIM allows
    > to set the minimum size of an extent to trim, ext4 stores the last
    > minimum extent size and only avoids trimming the group if it was
    > previously trimmed with minimum extent size equal to, or smaller than
    > the current call.
    >
    > There is currently no way to bypass the optimization without
    > umount/mount cycle. This becomes a problem when the file system is
    > live migrated to a different storage, because the optimization will
    > prevent possibly useful discard calls to the storage.
    >
    > Fix it by exporting the s_last_trim_minblks via sysfs interface which
    > will allow us to set the minimum size to the number of blocks larger
    > than subsequent FITRIM call, effectively bypassing the optimization.
    >
    > By setting the s_last_trim_minblks to ULONG_MAX the optimization will be
    > effectively cleared regardless of the previous state, or file system
    > configuration.
    >
    > For example:
    > getconf ULONG_MAX > /sys/fs/ext4/dm-1/last_trim_minblks
    >
    > Signed-off-by: Lukas Czerner <lczerner@redhat.com>
    > Reported-by: Laurent GUERBY <laurent@guerby.net>
    > Reviewed-by: Andreas Dilger <adilger@dilger.ca>
    > Link: https://lore.kernel.org/r/20211103145122.17338-2-lczerner@redhat.com
    > Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    > Signed-off-by: Sasha Levin <sashal@kernel.org>
    > ---
    > fs/ext4/sysfs.c | 2 ++
    > 1 file changed, 2 insertions(+)
    >
    > diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
    > index f24bef3be48a3..4192b4af10602 100644
    > --- a/fs/ext4/sysfs.c
    > +++ b/fs/ext4/sysfs.c
    > @@ -250,6 +250,7 @@ EXT4_ATTR(last_error_time, 0444, last_error_time);
    > EXT4_ATTR(journal_task, 0444, journal_task);
    > EXT4_RW_ATTR_SBI_UI(mb_prefetch, s_mb_prefetch);
    > EXT4_RW_ATTR_SBI_UI(mb_prefetch_limit, s_mb_prefetch_limit);
    > +EXT4_RW_ATTR_SBI_UL(last_trim_minblks, s_last_trim_minblks);
    >
    > static unsigned int old_bump_val = 128;
    > EXT4_ATTR_PTR(max_writeback_mb_bump, 0444, pointer_ui, &old_bump_val);
    > @@ -299,6 +300,7 @@ static struct attribute *ext4_attrs[] = {
    > #endif
    > ATTR_LIST(mb_prefetch),
    > ATTR_LIST(mb_prefetch_limit),
    > + ATTR_LIST(last_trim_minblks),
    > NULL,
    > };
    > ATTRIBUTE_GROUPS(ext4);
    > --
    > 2.34.1
    >

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