On Thu, Dec 14, 2023 at 5:29 AM Chengming Zhou
<zhouchengming@xxxxxxxxxxxxx> wrote:
>
> On 2023/12/14 07:24, Yosry Ahmed wrote:
> > On Tue, Dec 12, 2023 at 8:18 PM Chengming Zhou
> > <zhouchengming@xxxxxxxxxxxxx> wrote:
> >>
> >> In the !zpool_can_sleep_mapped() case such as zsmalloc, we need to first
> >> copy the entry->handle memory to a temporary memory, which is allocated
> >> using kmalloc.
> >>
> >> Obviously we can reuse the per-compressor dstmem to avoid allocating
> >> every time, since it's percpu-compressor and protected in mutex.
> >>
> >> Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
> >> Reviewed-by: Nhat Pham <nphamcs@xxxxxxxxx>
> >> ---
> >> mm/zswap.c | 29 +++++++++--------------------
> >> 1 file changed, 9 insertions(+), 20 deletions(-)
> >>
> >> diff --git a/mm/zswap.c b/mm/zswap.c
> >> index 7ee54a3d8281..edb8b45ed5a1 100644
> >> --- a/mm/zswap.c
> >> +++ b/mm/zswap.c
> >> @@ -1772,9 +1772,9 @@ bool zswap_load(struct folio *folio)
> >> struct zswap_entry *entry;
> >> struct scatterlist input, output;
> >> struct crypto_acomp_ctx *acomp_ctx;
> >> - u8 *src, *dst, *tmp;
> >> + unsigned int dlen = PAGE_SIZE;
> >> + u8 *src, *dst;
> >> struct zpool *zpool;
> >> - unsigned int dlen;
> >> bool ret;
> >>
> >> VM_WARN_ON_ONCE(!folio_test_locked(folio));
> >> @@ -1796,27 +1796,18 @@ bool zswap_load(struct folio *folio)
> >> goto stats;
> >> }
> >>
> >> - zpool = zswap_find_zpool(entry);
> >> - if (!zpool_can_sleep_mapped(zpool)) {
> >> - tmp = kmalloc(entry->length, GFP_KERNEL);
> >> - if (!tmp) {
> >> - ret = false;
> >> - goto freeentry;
> >> - }
> >> - }
> >> -
> >> /* decompress */
> >> - dlen = PAGE_SIZE;
> >> - src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
> >> + acomp_ctx = raw_cpu_ptr(entry->pool->acomp_ctx);
> >> + mutex_lock(acomp_ctx->mutex);
> >>
> >> + zpool = zswap_find_zpool(entry);
> >> + src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
> >> if (!zpool_can_sleep_mapped(zpool)) {
> >> - memcpy(tmp, src, entry->length);
> >> - src = tmp;
> >> + memcpy(acomp_ctx->dstmem, src, entry->length);
> >> + src = acomp_ctx->dstmem;
> >
> > I don't like that we are now using acomp_ctx->dstmem and
> > acomp_ctx->mutex now for purposes other than what the naming suggests.
>
> The "mutex" name is coherent, "dstmem" depends on how we use IMHO.
> Change to just "mem"? Or do you have a better name to replace?
>
> >
> > How about removing these two fields from acomp_ctx, and directly using
> > zswap_dstmem and zswap_mutex in both the load and store paths, rename
> > them, and add proper comments above their definitions that they are
> > for generic percpu buffering on the load and store paths?
>
> Yes, they are percpu memory and lock, but they are used by per acomp_ctx,
> and the cpu maybe changing in the middle, so maybe better to keep them.
I don't mean to remove completely. Keep them as (for example)
zswap_mem and zswap_mutex global percpu variables, and not have
pointers in acomp_ctx to them. Instead of using acomp_ctx->dstmem
today, we directly use the global zswap_mem (same for the mutex).
This makes it clear that the buffers are not owned or exclusively used
by the acomp_ctx. WDYT?
