| Message ID | 20220509131416.17553-10-linmiaohe@huawei.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | A few cleanup patches for swap | expand |
On Mon, 09 May 2022, Miaohe Lin wrote: > Use flags of si directly to check SWP_STABLE_WRITES to avoid possible > READ_ONCE and thus save some cpu cycles. > > Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> > --- > mm/memory.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 9c3e7e6ac202..89dd15504f3d 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -3892,7 +3892,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > */ > exclusive = true; > } else if (exclusive && PageWriteback(page) && > - (swp_swap_info(entry)->flags & SWP_STABLE_WRITES)) { > + (si->flags & SWP_STABLE_WRITES)) { Should this have a data_race() annotation. Other bit-tests of si->flags do because scan_swap_map_slots can update it asynchronously, but we know that won't matter in practice. Thanks, NeilBrown > /* > * This is tricky: not all swap backends support > * concurrent page modifications while under writeback. > -- > 2.23.0 > >
On 2022/5/10 8:28, NeilBrown wrote: > On Mon, 09 May 2022, Miaohe Lin wrote: >> Use flags of si directly to check SWP_STABLE_WRITES to avoid possible >> READ_ONCE and thus save some cpu cycles. >> >> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> >> --- >> mm/memory.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/memory.c b/mm/memory.c >> index 9c3e7e6ac202..89dd15504f3d 100644 >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -3892,7 +3892,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >> */ >> exclusive = true; >> } else if (exclusive && PageWriteback(page) && >> - (swp_swap_info(entry)->flags & SWP_STABLE_WRITES)) { >> + (si->flags & SWP_STABLE_WRITES)) { > > Should this have a data_race() annotation. Other bit-tests of si->flags > do because scan_swap_map_slots can update it asynchronously, but we know > that won't matter in practice. Yes, you're right. scan_swap_map_slots can update si->flags asynchronously while do_swap_page tests SWP_STABLE_WRITES here. We know this is harmless because SWP_STABLE_WRITES is only changed at swapon/swapoff. Will add data_race() annotation in next version to avoid possible KCSAN data-race complaint. Many thanks for pointing this out! :) > > Thanks, > NeilBrown > > >> /* >> * This is tricky: not all swap backends support >> * concurrent page modifications while under writeback. >> -- >> 2.23.0 >> >> > . >
On Tue, 10 May 2022 10:21:21 +0800 Miaohe Lin <linmiaohe@huawei.com> wrote: > On 2022/5/10 8:28, NeilBrown wrote: > > On Mon, 09 May 2022, Miaohe Lin wrote: > >> Use flags of si directly to check SWP_STABLE_WRITES to avoid possible > >> READ_ONCE and thus save some cpu cycles. > >> > >> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> > >> --- > >> mm/memory.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/mm/memory.c b/mm/memory.c > >> index 9c3e7e6ac202..89dd15504f3d 100644 > >> --- a/mm/memory.c > >> +++ b/mm/memory.c > >> @@ -3892,7 +3892,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > >> */ > >> exclusive = true; > >> } else if (exclusive && PageWriteback(page) && > >> - (swp_swap_info(entry)->flags & SWP_STABLE_WRITES)) { > >> + (si->flags & SWP_STABLE_WRITES)) { > > > > Should this have a data_race() annotation. Other bit-tests of si->flags > > do because scan_swap_map_slots can update it asynchronously, but we know > > that won't matter in practice. > > Yes, you're right. scan_swap_map_slots can update si->flags asynchronously while > do_swap_page tests SWP_STABLE_WRITES here. We know this is harmless because > SWP_STABLE_WRITES is only changed at swapon/swapoff. > > Will add data_race() annotation in next version to avoid possible KCSAN data-race complaint. > I did this: --- a/mm/memory.c~mm-swap-avoid-calling-swp_swap_info-when-try-to-check-swp_stable_writes-fix +++ a/mm/memory.c @@ -3889,7 +3889,7 @@ vm_fault_t do_swap_page(struct vm_fault */ exclusive = true; } else if (exclusive && PageWriteback(page) && - (si->flags & SWP_STABLE_WRITES)) { + data_race(si->flags & SWP_STABLE_WRITES)) { /* * This is tricky: not all swap backends support * concurrent page modifications while under writeback.
diff --git a/mm/memory.c b/mm/memory.c index 9c3e7e6ac202..89dd15504f3d 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3892,7 +3892,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) */ exclusive = true; } else if (exclusive && PageWriteback(page) && - (swp_swap_info(entry)->flags & SWP_STABLE_WRITES)) { + (si->flags & SWP_STABLE_WRITES)) { /* * This is tricky: not all swap backends support * concurrent page modifications while under writeback.
Use flags of si directly to check SWP_STABLE_WRITES to avoid possible READ_ONCE and thus save some cpu cycles. Signed-off-by: Miaohe Lin <linmiaohe@huawei.com> --- mm/memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)