On 2024/2/16 16:23, Yosry Ahmed wrote:
> On Fri, Feb 16, 2024 at 04:05:39PM +1300, Barry Song wrote:
>> From: Barry Song <v-songbaohua@xxxxxxxx>
>>
>> My commit fc8580edbaa6 ("mm: zsmalloc: return -ENOSPC rather than -EINVAL
>> in zs_malloc while size is too large") wanted to depend on zs_malloc's
>> returned ENOSPC to distinguish the case that compressed data is larger
>> than the original data from normal compression cases. The commit, for
>> sure, was correct and worked as expected but the code wouldn't run to
>> there after commit 744e1885922a ("crypto: scomp - fix req->dst buffer
>> overflow") as Chengming's this patch makes zswap_store() goto out
>> immediately after the special compression case happens. So there is
>> no chance to execute zs_malloc() now. We need to fix the count right
>> after compressions return ENOSPC.
>>
>> Fixes: fc8580edbaa6 ("mm: zsmalloc: return -ENOSPC rather than -EINVAL in zs_malloc while size is too large")
>
> I don't see how this is a fix for that commit. Commit fc8580edbaa6 made
> sure zsmalloc returns a correct errno when the compressed size is too
> large. The fact that zswap stores were failing before calling into
> zsmalloc and not reporting the error correctly in debug counters is not
> that commits fault.
>
> I think the proper fixes should be 744e1885922a if it introduced the
> first scenario where -ENOSPC can be returned from scomp without handling
> it properly in zswap. If -ENOSPC was a possible return value before
> that, then it should be cb61dad80fdc ("zswap: export compression failure
> stats"), where the counter was introduced.
Right, 744e1885922a maybe a better fixes target.
>
>> Cc: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
>> Cc: Nhat Pham <nphamcs@xxxxxxxxx>
>> Cc: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
>> Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
>> ---
>> mm/zswap.c | 5 ++++-
>> 1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/zswap.c b/mm/zswap.c
>> index 6319d2281020..9a21dbe8c056 100644
>> --- a/mm/zswap.c
>> +++ b/mm/zswap.c
>> @@ -1627,7 +1627,10 @@ bool zswap_store(struct folio *folio)
>> dlen = acomp_ctx->req->dlen;
>>
>> if (ret) {
>> - zswap_reject_compress_fail++;
>> + if (ret == -ENOSPC)
>> + zswap_reject_compress_poor++;
>> + else
>> + zswap_reject_compress_fail++;
>
> With this diff, we have four locations in zswap_store() where we
> increment zswap_reject_compress_{poor/fail}.
>
> How about the following instead?A
>
> diff --git a/mm/zswap.c b/mm/zswap.c
> index 62fe307521c93..3a7e8ba7f6116 100644
> --- a/mm/zswap.c
> +++ b/mm/zswap.c
> @@ -1059,24 +1059,16 @@ static bool zswap_compress(struct folio *folio, struct zswap_entry *entry)
> */
> ret = crypto_wait_req(crypto_acomp_compress(acomp_ctx->req), &acomp_ctx->wait);
> dlen = acomp_ctx->req->dlen;
> - if (ret) {
> - zswap_reject_compress_fail++;
> + if (ret)
> goto unlock;
> - }
>
> zpool = zswap_find_zpool(entry);
> gfp = __GFP_NORETRY | __GFP_NOWARN | __GFP_KSWAPD_RECLAIM;
> if (zpool_malloc_support_movable(zpool))
> gfp |= __GFP_HIGHMEM | __GFP_MOVABLE;
> ret = zpool_malloc(zpool, dlen, gfp, &handle);
> - if (ret == -ENOSPC) {
> - zswap_reject_compress_poor++;
> - goto unlock;
> - }
> - if (ret) {
> - zswap_reject_alloc_fail++;
> + if (ret)
> goto unlock;
> - }
>
> buf = zpool_map_handle(zpool, handle, ZPOOL_MM_WO);
> memcpy(buf, dst, dlen);
> @@ -1086,6 +1078,10 @@ static bool zswap_compress(struct folio *folio, struct zswap_entry *entry)
> entry->length = dlen;
>
> unlock:
> + if (ret == -ENOSPC)
> + zswap_reject_compress_poor++;
> + else if (ret)
> + zswap_reject_alloc_fail++;
Here have two cases: zswap_reject_compress_fail, zswap_reject_alloc_fail.
> mutex_unlock(&acomp_ctx->mutex);
> return ret == 0;
> }
>
>> goto put_dstmem;
>> }
>>
>> --
>> 2.34.1
>>
