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target: Don't zero pages used for data buffers 

Doing alloc_page(GFP_KERNEL | __GFP_ZERO) to get pages used for data
buffers wastes a lot of CPU clearing pages that will be quickly be
overwritten by the actual data.  However, for emulated control
commands such as INQUIRY and so on, the code does assume that the
buffer is zeroed.

To avoid this CPU overhead, skip the __GFP_ZERO for commands that are
actually moving data, ie cmds that have SCF_SCSI_DATA_SG_IO_CDB set.

Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
This commit is contained in:
roland@purestorage.com 2012-01-04 15:59:58 -08:00 committed by Nicholas Bellinger
parent 6816966a84
commit 9db9da3322
1 changed files with 4 additions and 1 deletions
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5
drivers/target/target_core_transport.c
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@ -3516,6 +3516,7 @@ transport_generic_get_mem(struct se_cmd *cmd)
u32 length = cmd->data_length;
unsigned int nents;
struct page *page;
gfp_t zero_flag;
int i = 0;
nents = DIV_ROUND_UP(length, PAGE_SIZE);
@ -3526,9 +3527,11 @@ transport_generic_get_mem(struct se_cmd *cmd)
cmd->t_data_nents = nents;
sg_init_table(cmd->t_data_sg, nents);
zero_flag = cmd->se_cmd_flags & SCF_SCSI_DATA_SG_IO_CDB ? 0 : __GFP_ZERO;
while (length) {
u32 page_len = min_t(u32, length, PAGE_SIZE);
page = alloc_page(GFP_KERNEL | __GFP_ZERO);
page = alloc_page(GFP_KERNEL | zero_flag);
if (!page)
goto out;