> From: Wanpeng Li [mailto:[email protected]]
> Subject: [PATCH 02/10] staging: zcache: remove zcache_freeze
>
> The default value of zcache_freeze is false and it won't be modified by
> other codes. Remove zcache_freeze since no routine can disable zcache
> during system running.
>
> Signed-off-by: Wanpeng Li <[email protected]>
I'd prefer to leave this code in place as it may be very useful
if/when zcache becomes more tightly integrated into the MM subsystem
and the rest of the kernel. And the subtleties for temporarily disabling
zcache (which is what zcache_freeze does) are non-obvious and
may cause data loss so if someone wants to add this functionality
back in later and don't have this piece of code, it may take
a lot of pain to get it working.
Usage example: All CPUs are fully saturated so it is questionable
whether spending CPU cycles for compression is wise. Kernel
could disable zcache using zcache_freeze. (Yes, a new entry point
would need to be added to enable/disable zcache_freeze.)
My two cents... others are welcome to override.
> ---
> drivers/staging/zcache/zcache-main.c | 55
> +++++++++++-----------------------
> 1 file changed, 18 insertions(+), 37 deletions(-)
>
> diff --git a/drivers/staging/zcache/zcache-main.c
> b/drivers/staging/zcache/zcache-main.c
> index e23d814..fe6801a 100644
> --- a/drivers/staging/zcache/zcache-main.c
> +++ b/drivers/staging/zcache/zcache-main.c
> @@ -1118,15 +1118,6 @@ free_and_out:
> #endif /* CONFIG_ZCACHE_WRITEBACK */
>
> /*
> - * When zcache is disabled ("frozen"), pools can be created and destroyed,
> - * but all puts (and thus all other operations that require memory
> allocation)
> - * must fail. If zcache is unfrozen, accepts puts, then frozen again,
> - * data consistency requires all puts while frozen to be converted into
> - * flushes.
> - */
> -static bool zcache_freeze;
> -
> -/*
> * This zcache shrinker interface reduces the number of ephemeral pageframes
> * used by zcache to approximately the same as the total number of LRU_FILE
> * pageframes in use, and now also reduces the number of persistent
> pageframes
> @@ -1221,44 +1212,34 @@ int zcache_put_page(int cli_id, int pool_id, struct
> tmem_oid *oidp,
> {
> struct tmem_pool *pool;
> struct tmem_handle th;
> - int ret = -1;
> + int ret = 0;
> void *pampd = NULL;
>
> BUG_ON(!irqs_disabled());
> pool = zcache_get_pool_by_id(cli_id, pool_id);
> if (unlikely(pool == NULL))
> goto out;
> - if (!zcache_freeze) {
> - ret = 0;
> - th.client_id = cli_id;
> - th.pool_id = pool_id;
> - th.oid = *oidp;
> - th.index = index;
> - pampd = zcache_pampd_create((char *)page, size, raw,
> - ephemeral, &th);
> - if (pampd == NULL) {
> - ret = -ENOMEM;
> - if (ephemeral)
> - inc_zcache_failed_eph_puts();
> - else
> - inc_zcache_failed_pers_puts();
> - } else {
> - if (ramster_enabled)
> - ramster_do_preload_flnode(pool);
> - ret = tmem_put(pool, oidp, index, 0, pampd);
> - if (ret < 0)
> - BUG();
> - }
> - zcache_put_pool(pool);
> +
> + th.client_id = cli_id;
> + th.pool_id = pool_id;
> + th.oid = *oidp;
> + th.index = index;
> + pampd = zcache_pampd_create((char *)page, size, raw,
> + ephemeral, &th);
> + if (pampd == NULL) {
> + ret = -ENOMEM;
> + if (ephemeral)
> + inc_zcache_failed_eph_puts();
> + else
> + inc_zcache_failed_pers_puts();
> } else {
> - inc_zcache_put_to_flush();
> if (ramster_enabled)
> ramster_do_preload_flnode(pool);
> - if (atomic_read(&pool->obj_count) > 0)
> - /* the put fails whether the flush succeeds or not */
> - (void)tmem_flush_page(pool, oidp, index);
> - zcache_put_pool(pool);
> + ret = tmem_put(pool, oidp, index, 0, pampd);
> + if (ret < 0)
> + BUG();
> }
> + zcache_put_pool(pool);
> out:
> return ret;
> }
> --
> 1.7.10.4
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