| Message ID | be0aba0f61ea5c583ea696db4cc621d3886893de.1547624239.git.yi.z.zhang@linux.intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | support MAP_SYNC for memory-backend-file | expand |
On Wed, Jan 16, 2019 at 04:11:16PM +0800, Zhang Yi wrote: > Signed-off-by: Zhang Yi <yi.z.zhang@linux.intel.com> > --- > docs/nvdimm.txt | 21 ++++++++++++++++++++- > qemu-options.hx | 4 ++++ > 2 files changed, 24 insertions(+), 1 deletion(-) > > diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt > index 5f158a6..565ba73 100644 > --- a/docs/nvdimm.txt > +++ b/docs/nvdimm.txt > @@ -142,11 +142,30 @@ backend of vNVDIMM: > Guest Data Persistence > ---------------------- > > +vNVDIMM is designed and implemented to guarantee the guest data > +persistence on the backends even on the host crash and power in case of a host crash or a power failure (be consistent) > +failures. However, there are still some requirements and limitations > +as explained below. > + > Though QEMU supports multiple types of vNVDIMM backends on Linux, > -currently the only one that can guarantee the guest write persistence > +if MAP_SYNC is not supported by the host kernel and the backends, > +the only backend that can guarantee the guest write persistence > is the device DAX on the real NVDIMM device (e.g., /dev/dax0.0), to > which all guest access do not involve any host-side kernel cache. > > +mmap(2) flag MAP_SYNC is added since Linux kernel 4.15. On such > +systems, QEMU can mmap(2) the backend with MAP_SYNC, which can ensure which ensures > +filesystem metadata consistent consistency > even after a system crash or power a power > +failure. Besides the host kernel support, enabling MAP_SYNC in QEMU > +also requires: > + > + - the backend is a file supporting DAX, e.g., a file on an ext4 or > + xfs file system mounted with '-o dax', > + > + - 'share' option of memory-backend-file is 'on'. why does share need to be on? > + > + - 'pmem' option of memory-backend-file is 'on' > + > When using other types of backends, it's suggested to set 'unarmed' > option of '-device nvdimm' to 'on', which sets the unarmed flag of the > guest NVDIMM region mapping structure. This unarmed flag indicates > diff --git a/qemu-options.hx b/qemu-options.hx > index 08f8516..545cb8a 100644 > --- a/qemu-options.hx > +++ b/qemu-options.hx > @@ -4002,6 +4002,10 @@ using the SNIA NVM programming model (e.g. Intel NVDIMM). > If @option{pmem} is set to 'on', QEMU will take necessary operations to > guarantee the persistence of its own writes to @option{mem-path} > (e.g. in vNVDIMM label emulation and live migration). > +Also, we will map the backend-file with MAP_SYNC flag, which can ensure > +the file metadata is in sync to @option{mem-path} even on the host crash > +and power failures. MAP_SYNC requires supports from both the host kernel requires support > +(since Linux kernel 4.15) and @option{mem-path} (only files supporting DAX). > > @item -object memory-backend-ram,id=@var{id},merge=@var{on|off},dump=@var{on|off},share=@var{on|off},prealloc=@var{on|off},size=@var{size},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave} > > -- > 2.7.4
On 2019-01-16 at 10:40:23 -0500, Michael S. Tsirkin wrote: > On Wed, Jan 16, 2019 at 04:11:16PM +0800, Zhang Yi wrote: > > Signed-off-by: Zhang Yi <yi.z.zhang@linux.intel.com> > > --- > > docs/nvdimm.txt | 21 ++++++++++++++++++++- > > qemu-options.hx | 4 ++++ > > 2 files changed, 24 insertions(+), 1 deletion(-) > > > > diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt > > index 5f158a6..565ba73 100644 > > --- a/docs/nvdimm.txt > > +++ b/docs/nvdimm.txt > > @@ -142,11 +142,30 @@ backend of vNVDIMM: > > Guest Data Persistence > > ---------------------- > > > > +vNVDIMM is designed and implemented to guarantee the guest data > > +persistence on the backends even on the host crash and power > > in case of a host crash or a power failure > > (be consistent) > > > +failures. However, there are still some requirements and limitations > > +as explained below. > > + > > Though QEMU supports multiple types of vNVDIMM backends on Linux, > > -currently the only one that can guarantee the guest write persistence > > +if MAP_SYNC is not supported by the host kernel and the backends, > > +the only backend that can guarantee the guest write persistence > > is the device DAX on the real NVDIMM device (e.g., /dev/dax0.0), to > > which all guest access do not involve any host-side kernel cache. > > > > +mmap(2) flag MAP_SYNC is added since Linux kernel 4.15. On such > > +systems, QEMU can mmap(2) the backend with MAP_SYNC, which can ensure > > which ensures > > > +filesystem metadata consistent > > consistency > > > even after a system crash or power > > a power > > > +failure. Besides the host kernel support, enabling MAP_SYNC in QEMU > > +also requires: > > + > > + - the backend is a file supporting DAX, e.g., a file on an ext4 or > > + xfs file system mounted with '-o dax', > > + > > + - 'share' option of memory-backend-file is 'on'. > > why does share need to be on? According to mmap(2) man page, MAP_SYNC is available only with the MAP_SHARED_VALIDATE map‐ping type. I will add this to documentation, Thanks. > > > + > > + - 'pmem' option of memory-backend-file is 'on' > > + > > When using other types of backends, it's suggested to set 'unarmed' > > option of '-device nvdimm' to 'on', which sets the unarmed flag of the > > guest NVDIMM region mapping structure. This unarmed flag indicates > > diff --git a/qemu-options.hx b/qemu-options.hx > > index 08f8516..545cb8a 100644 > > --- a/qemu-options.hx > > +++ b/qemu-options.hx > > @@ -4002,6 +4002,10 @@ using the SNIA NVM programming model (e.g. Intel NVDIMM). > > If @option{pmem} is set to 'on', QEMU will take necessary operations to > > guarantee the persistence of its own writes to @option{mem-path} > > (e.g. in vNVDIMM label emulation and live migration). > > +Also, we will map the backend-file with MAP_SYNC flag, which can ensure > > +the file metadata is in sync to @option{mem-path} even on the host crash > > +and power failures. MAP_SYNC requires supports from both the host kernel > > requires support > > > +(since Linux kernel 4.15) and @option{mem-path} (only files supporting DAX). > > > > @item -object memory-backend-ram,id=@var{id},merge=@var{on|off},dump=@var{on|off},share=@var{on|off},prealloc=@var{on|off},size=@var{size},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave} > > > > -- > > 2.7.4
> > > --- > > > docs/nvdimm.txt | 21 ++++++++++++++++++++- > > > qemu-options.hx | 4 ++++ > > > 2 files changed, 24 insertions(+), 1 deletion(-) > > > > > > diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt > > > index 5f158a6..565ba73 100644 > > > --- a/docs/nvdimm.txt > > > +++ b/docs/nvdimm.txt > > > @@ -142,11 +142,30 @@ backend of vNVDIMM: > > > Guest Data Persistence > > > ---------------------- > > > > > > +vNVDIMM is designed and implemented to guarantee the guest data > > > +persistence on the backends even on the host crash and power > > > > in case of a host crash or a power failure > > > > (be consistent) > > > > > +failures. However, there are still some requirements and limitations > > > +as explained below. > > > + > > > Though QEMU supports multiple types of vNVDIMM backends on Linux, > > > -currently the only one that can guarantee the guest write persistence > > > +if MAP_SYNC is not supported by the host kernel and the backends, > > > +the only backend that can guarantee the guest write persistence > > > is the device DAX on the real NVDIMM device (e.g., /dev/dax0.0), to > > > which all guest access do not involve any host-side kernel cache. > > > > > > +mmap(2) flag MAP_SYNC is added since Linux kernel 4.15. On such > > > +systems, QEMU can mmap(2) the backend with MAP_SYNC, which can ensure > > > > which ensures > > > > > +filesystem metadata consistent > > > > consistency > > > > > even after a system crash or power > > > > a power > > > > > +failure. Besides the host kernel support, enabling MAP_SYNC in QEMU > > > +also requires: > > > + > > > + - the backend is a file supporting DAX, e.g., a file on an ext4 or > > > + xfs file system mounted with '-o dax', > > > + > > > + - 'share' option of memory-backend-file is 'on'. > > > > why does share need to be on? > According to mmap(2) man page, > MAP_SYNC is available only with the MAP_SHARED_VALIDATE map‐ping type. > I will add this to documentation, Thanks. MAP_SHARE_VALIDATE should be used to validate MAP_SYNC with MAP_SHARED. #define MAP_SHARED_VALIDATE 0x03 In contrast, MAP_SHARED is: #define MAP_SHARED 0x01 /* Share changes */ I think we should use MAP_SHARED_VALIDATE with MAP_SYNC here? Thanks, Pankaj > > > > > + > > > + - 'pmem' option of memory-backend-file is 'on' > > > + > > > When using other types of backends, it's suggested to set 'unarmed' > > > option of '-device nvdimm' to 'on', which sets the unarmed flag of the > > > guest NVDIMM region mapping structure. This unarmed flag indicates > > > diff --git a/qemu-options.hx b/qemu-options.hx > > > index 08f8516..545cb8a 100644 > > > --- a/qemu-options.hx > > > +++ b/qemu-options.hx > > > @@ -4002,6 +4002,10 @@ using the SNIA NVM programming model (e.g. Intel > > > NVDIMM). > > > If @option{pmem} is set to 'on', QEMU will take necessary operations to > > > guarantee the persistence of its own writes to @option{mem-path} > > > (e.g. in vNVDIMM label emulation and live migration). > > > +Also, we will map the backend-file with MAP_SYNC flag, which can ensure > > > +the file metadata is in sync to @option{mem-path} even on the host crash > > > +and power failures. MAP_SYNC requires supports from both the host kernel > > > > requires support > > > > > +(since Linux kernel 4.15) and @option{mem-path} (only files supporting > > > DAX). > > > > > > @item -object > > > memory-backend-ram,id=@var{id},merge=@var{on|off},dump=@var{on|off},share=@var{on|off},prealloc=@var{on|off},size=@var{size},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave} > > > > > > -- > > > 2.7.4 >
On 2019-01-21 at 02:21:39 -0500, Pankaj Gupta wrote: > > > > > --- > > > > docs/nvdimm.txt | 21 ++++++++++++++++++++- > > > > qemu-options.hx | 4 ++++ > > > > 2 files changed, 24 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt > > > > index 5f158a6..565ba73 100644 > > > > --- a/docs/nvdimm.txt > > > > +++ b/docs/nvdimm.txt > > > > @@ -142,11 +142,30 @@ backend of vNVDIMM: > > > > Guest Data Persistence > > > > ---------------------- > > > > > > > > +vNVDIMM is designed and implemented to guarantee the guest data > > > > +persistence on the backends even on the host crash and power > > > > > > in case of a host crash or a power failure > > > > > > (be consistent) > > > > > > > +failures. However, there are still some requirements and limitations > > > > +as explained below. > > > > + > > > > Though QEMU supports multiple types of vNVDIMM backends on Linux, > > > > -currently the only one that can guarantee the guest write persistence > > > > +if MAP_SYNC is not supported by the host kernel and the backends, > > > > +the only backend that can guarantee the guest write persistence > > > > is the device DAX on the real NVDIMM device (e.g., /dev/dax0.0), to > > > > which all guest access do not involve any host-side kernel cache. > > > > > > > > +mmap(2) flag MAP_SYNC is added since Linux kernel 4.15. On such > > > > +systems, QEMU can mmap(2) the backend with MAP_SYNC, which can ensure > > > > > > which ensures > > > > > > > +filesystem metadata consistent > > > > > > consistency > > > > > > > even after a system crash or power > > > > > > a power > > > > > > > +failure. Besides the host kernel support, enabling MAP_SYNC in QEMU > > > > +also requires: > > > > + > > > > + - the backend is a file supporting DAX, e.g., a file on an ext4 or > > > > + xfs file system mounted with '-o dax', > > > > + > > > > + - 'share' option of memory-backend-file is 'on'. > > > > > > why does share need to be on? > > According to mmap(2) man page, > > MAP_SYNC is available only with the MAP_SHARED_VALIDATE map‐ping type. > > I will add this to documentation, Thanks. > > MAP_SHARE_VALIDATE should be used to validate MAP_SYNC with MAP_SHARED. > > #define MAP_SHARED_VALIDATE 0x03 > > In contrast, MAP_SHARED is: > #define MAP_SHARED 0x01 /* Share changes */ > > I think we should use MAP_SHARED_VALIDATE with MAP_SYNC here? > > Thanks, > Pankaj Yes, Pankaj, Thanks point that out, I will add the MAP_SHARED_VALIDATE. > > > > > > > > + > > > > + - 'pmem' option of memory-backend-file is 'on' > > > > + > > > > When using other types of backends, it's suggested to set 'unarmed' > > > > option of '-device nvdimm' to 'on', which sets the unarmed flag of the > > > > guest NVDIMM region mapping structure. This unarmed flag indicates > > > > diff --git a/qemu-options.hx b/qemu-options.hx > > > > index 08f8516..545cb8a 100644 > > > > --- a/qemu-options.hx > > > > +++ b/qemu-options.hx > > > > @@ -4002,6 +4002,10 @@ using the SNIA NVM programming model (e.g. Intel > > > > NVDIMM). > > > > If @option{pmem} is set to 'on', QEMU will take necessary operations to > > > > guarantee the persistence of its own writes to @option{mem-path} > > > > (e.g. in vNVDIMM label emulation and live migration). > > > > +Also, we will map the backend-file with MAP_SYNC flag, which can ensure > > > > +the file metadata is in sync to @option{mem-path} even on the host crash > > > > +and power failures. MAP_SYNC requires supports from both the host kernel > > > > > > requires support > > > > > > > +(since Linux kernel 4.15) and @option{mem-path} (only files supporting > > > > DAX). > > > > > > > > @item -object > > > > memory-backend-ram,id=@var{id},merge=@var{on|off},dump=@var{on|off},share=@var{on|off},prealloc=@var{on|off},size=@var{size},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave} > > > > > > > > -- > > > > 2.7.4 > >
diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt index 5f158a6..565ba73 100644 --- a/docs/nvdimm.txt +++ b/docs/nvdimm.txt @@ -142,11 +142,30 @@ backend of vNVDIMM: Guest Data Persistence ---------------------- +vNVDIMM is designed and implemented to guarantee the guest data +persistence on the backends even on the host crash and power +failures. However, there are still some requirements and limitations +as explained below. + Though QEMU supports multiple types of vNVDIMM backends on Linux, -currently the only one that can guarantee the guest write persistence +if MAP_SYNC is not supported by the host kernel and the backends, +the only backend that can guarantee the guest write persistence is the device DAX on the real NVDIMM device (e.g., /dev/dax0.0), to which all guest access do not involve any host-side kernel cache. +mmap(2) flag MAP_SYNC is added since Linux kernel 4.15. On such +systems, QEMU can mmap(2) the backend with MAP_SYNC, which can ensure +filesystem metadata consistent even after a system crash or power +failure. Besides the host kernel support, enabling MAP_SYNC in QEMU +also requires: + + - the backend is a file supporting DAX, e.g., a file on an ext4 or + xfs file system mounted with '-o dax', + + - 'share' option of memory-backend-file is 'on'. + + - 'pmem' option of memory-backend-file is 'on' + When using other types of backends, it's suggested to set 'unarmed' option of '-device nvdimm' to 'on', which sets the unarmed flag of the guest NVDIMM region mapping structure. This unarmed flag indicates diff --git a/qemu-options.hx b/qemu-options.hx index 08f8516..545cb8a 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -4002,6 +4002,10 @@ using the SNIA NVM programming model (e.g. Intel NVDIMM). If @option{pmem} is set to 'on', QEMU will take necessary operations to guarantee the persistence of its own writes to @option{mem-path} (e.g. in vNVDIMM label emulation and live migration). +Also, we will map the backend-file with MAP_SYNC flag, which can ensure +the file metadata is in sync to @option{mem-path} even on the host crash +and power failures. MAP_SYNC requires supports from both the host kernel +(since Linux kernel 4.15) and @option{mem-path} (only files supporting DAX). @item -object memory-backend-ram,id=@var{id},merge=@var{on|off},dump=@var{on|off},share=@var{on|off},prealloc=@var{on|off},size=@var{size},host-nodes=@var{host-nodes},policy=@var{default|preferred|bind|interleave}
Signed-off-by: Zhang Yi <yi.z.zhang@linux.intel.com> --- docs/nvdimm.txt | 21 ++++++++++++++++++++- qemu-options.hx | 4 ++++ 2 files changed, 24 insertions(+), 1 deletion(-)